I am reading "America's Longest War" by George Herring and a few trends are sticking out to me.
It seems that the greatest obstacle to US success in Vietnam, once committed, was that the South Vietnamese government, from Diem on to the military Junta and onwards, was extremely ineffective, authoritarian, and unpopular. It seemed to be failing in several key aspects. First was its policy on human rights, particularly among religious groups such as the Catholics and the Buddhists. Second was its inability to convince the South Vietnamese population that Communism was not a desirable state of affairs: with a great deal of success, the Communists were able to infiltrate and receive a broad base of support within the South Vietnamese peasantry due to South Vietnam's ineffectiveness in providing any tangible land reform, democratic reform, or general social development. Third, the North Vietnamese in a sense had a moral high ground among the population, as they were able to successfully portray themselves as being the 'anti-imperialist' faction and the South Vietnamese as puppets to a new master (having just defeated the French, this sentiment was running high.) All in all, it seemed that no matter how much the US threw at the North and against the Viet Cong, without a unified, committed, and effective South Vietnamese government and population, it was all an exercise in futility.
Therefore, could a better strategy for the USA, perhaps after the assassination of Diem where the USA could have installed a more cooperative government, have been something like:
Promote the strategic hamlets program in a major sense, with much more planning, resources, and thought put into it. Ensure the provision of actual security, in combination with real localist democratic reforms, land reform, and economic reforms to win support of the rural peasantry, and therefore resist Communist infiltration / support
Engage in more counter-insurgency, social development, and 'hearts and minds' efforts rather than strategic bombing
Enforce a policy of religious toleration and cease the harassment and discrimination towards religious minorities
Encourage the South Vietnamese Army and other Allies (South Korea, Japan, Australia, etc) to take a much more public and involved role with the war, thus avoiding charges of this being an 'American war'
Promote the role of the military / engage in 'coup-proofing' to ensure the stability of the current regime
End strategic bombing in the South, while ramping it up heavily on the North, as opposed to the gradualist approach taken by Johnson and Operation Rolling Thunder
Securing the Ho Chi Minh trail early to blunt North Vietnamese infiltration and harassment attempts
I suppose that theoretically anything is possible, but is there any source that you can think of that would perhaps give me more insight into whether such an approach would have been operationally implementable, strategically sound, and / or advantageous towards the US strategic objective of ensuring a non-Communist, independent South Vietnam?
Was there any way to win that war?
All the options you count up could have led to far more positive results and perhaps even a victory in the Vietnam War. Most scholars dealing with counterinsurgency would identify many of your points as being vital misses during the Vietnam War.
However, that's not how things turned out and while I am bound by the rules of this subreddit not to speculate about a possible victory in Vietnam, it is fair to say that history is a very complex matter. While you and I might think that yes, engaging in civic actions on a larger scale would have made the rural population of South Vietnam more inclined to turn towards the South Vietnamese government, the truth of the matter is that there are so many small variables that could have changed things in unexpected ways.
Instead of playing 'what if', I will recommend you three sources dealing with the topic of the Vietnam War and counterinsurgency (and which I am sure will be able to answer your answer):
Triumph Forsaken: The Vietnam War, 1954-1965 by Mark Moyar (Cambridge University Press, 2009). This book is written by a revisionist Vietnam War historian and is in my opinion a must-read for anyone who is interested in modern scholarship on the Vietnam War. This book argues against many of the established orthodox historians of the Vietnam War and is bound to make you rethink what you've always thought about the war (and South Vietnam in general).
Learning to Eat Soup with a Knife: Counterinsurgency Lessons from Malaya and Vietnam by John A. Nagl (The University of Chicago Press, 2005). Nagl's seminal book is a comparison between the counterinsurgency efforts carried out by the British in Malaya and the Americans in Vietnam. While heavily on the military, it is still one of the most important and easily accessible books on counterinsurgency written. This should give you some answers whether or not a counterinsurgency implementation or an ARVN reformation might have led to a desired result.
Lastly, Westmoreland's War: Reassessing American Strategy in Vietnam by Gregory Daddis (Oxford University Press, 2014). I include this book because it is supposed to work as a counterargument to Nagl above. Daddis' reassessment of the American strategy during the Vietnam War questions the revisionist perspective and is an interesting read. While I might not agree with his views, it is still required reading if you want to understand the viability of some of your points.
Encourage the South Vietnamese Army and other Allies (South Korea, Japan, Australia, etc) to take a much more public and involved role with the war, thus avoiding charges of this being an 'American war'
A couple of notes regarding Korea and Japan. South Korea did, in fact, send soldiers to fight in Vietnam. Park Chung-hee did this for a few reasons - valuable combat experience, to keep the US happy and in Korea, and to use it as a negotiating tool with the US. Not only did South Korea send soldiers, but those soldiers have been accused of being some of the most brutal towards civilians, to the point where there are groups today in South Korea that specialize in helping Vietnam as a sort of atonement for the past.
Japan, on the other hand, was strictly forbidden from deploying troops overseas as per their American-imposed post WWII pacifist constitution, a constitutional requirement that has stood until just a few weeks ago.
There is an understandable contradiction in your question. As you note, the war always depended on an outcome where the RVN prevailed over the NLF/PLAF/Viet Cong and North Vietnamese armed forces. In this sense, no the U.S. could not have won the war.
I also want to push you to re-think some of your points, and more so to rethink what limits are inherent in the book you read and its author. First, authoritarianism alone or un-popularity are not sufficient stand alone explanations for the collapse of the Diem government. After all, refugees continually fled the control of the Democratic Republic of Vietnam, particularly from 1949 onwards. A million Vietnamese chose to relocate to the non-communist State of Vietnam after the 1954 Geneva Accords. Freedom of press, academic freedoms, political expression, and basic liberty were severely circumscribed in the DRV/North Vietnam. People did not like this. They rioted, went to jail, and led local rebellions, etc. You do not hear about those things in Herring. They increasingly controlled religious groups with absolute authority to the point that the leadership of these groups were subordinate to the communist party or members themselves. Does this rehabilitate Diem? No. But it prompts us to think more critically and comparatively.
What eventually pacified Vietnam was the incarceration by the DRV/Socialist Republic of Vietnam of several hundred thousand political opponents for an extended period. That was never something attempted by South Vietnam. Those liberal student groups protesting the RVN in Saigon also quickly found themselves at odds with the new government, but had little freedom to express it as they had a few years earlier. Furthermore, the economic situation precipitously dropped after 1975 and it wasn't until the 1990s, after the SRV had adopted a liberal market philosophy, that southerners recovered to levels commensurate with pre 1975.
Once again, I want to question from whose perspective did the North Vietnamese have the moral superiority? From Herring and other western writers? Certainly. That was how they explained the troubles of the State of Vietnam and its successor the Republic of Vietnam. But as I've noted many Vietnamese still chose to go to the other side. Even as the siege of Dien Bien Phu was underway, Vietnamese crossed sides both ways. When the Viet Minh/ DRV stormed Dien Bien Phu, remember that they captured more Vietnamese fighting for the State of Vietnam than they did Frenchmen. Indeed, in a throwback to WWI, Giap had to order the execution of soldiers who refused to engage in human wave tactics at Dien Bien Phu.
Assigning an overwhelming moral superiority to the North misses the point. It was contested. We have copious information on the U.S. side of things, but very little about the RVN and DRV. As some historians of counterinsurgency argue, hearts and minds are a distant second to attacking the literal hearts and minds. Assassinations, forced relocations of populations, and other coercive measures are often more important in deciding outcomes. Thousands of government officials or simply those neutral to the NLF are executed (the converse is true as well, with RVN officials killing NFL/PLAF functionaries). This is important in explaining events, rather than an inherent moral superiority. That is constructed independently.