The progression of the American Revolution and how it exactly became a revolution can sometimes be a bit stagnating. You’ve pretty much nailed some of the military aspects of Great Britain at the time, they certainly were not to be messed with, so to speak. But these aspects are easier to see in hindsight. I'd like to tackle this with a bit of the military points you bring up and the rest I'll address as to the general sentiments in 1775 becoming the foundation for why war will become the primary viable option.

I’m currently engrossed in bios of George Washington for the military planning portions of my American Revolution research, and although the sheer might of Britain was well realized once the war commenced, certain aspects were thought to be advantages to the colonies. The concentration of British troops in New England was thought to be manageable if sieges on their positions proved successful by the end of the year (1775). This would allow important ports to be taken and the British reinforcements to be cut out, a hope by some to end the “war” early and re-affirm the colonist’s demands as British subjects. The Siege of Boston replicated this plan, although the city was not reclaimed in time for hostilities to end in the near future. (Ferling's The First of Men: A Life of George Washington)

And a few quick bullet points as far as Britain’s inherent disadvantages that the colonists utilized:

• American home turf advantage in addition to the colonies massive size would prove to be difficult to contain by the British.

• Possible intervention in the conflict from other American-colonial seeking world powers (ex: the French & Dutch)

• Regardless of Continental Army professionalism/training, had a large pool of citizens to call from to replenish the army (a great population to draw from statistically speaking, although the army actually had many reinforcement issues throughout the war)

All that aside, you ask why did they take the risk? Who in their right mind - even given the hopes to end the war early while Britain was getting ahold of the manpower to dedicate to the suppression - would attempt this? Not to be quote crazy, but I can think of no better way to directly describe the reasoning behind these actions than from the Declaration of the Causes and Necessity of Taking Up Arms (1775)

"The legislature of Great-Britain, however, stimulated by an inordinate passion for a power not only unjustifiable, but which they know to be peculiarly reprobated by the very constitution of that kingdom . . . attempted to effect their cruel and impolitic purpose of enslaving these colonies by violence, and have thereby rendered it necessary for us to close with their last appeal from reason to arms”

and

"They have undertaken to give and grant our money without our consent . . . statutes have been passed for extending the jurisdiction of courts of admiralty and vice-admiralty beyond their ancient limits; for depriving us of the accustomed and inestimable privilege of trial by jury, in cases affecting both life and property; for suspending the legislature of one of the colonies; for interdicting all commerce to the capital of another; and for altering fundamentally the form of government established by charter, and secured by acts of its own legislature solemnly confirmed by the crown; for exempting the "murderers" of colonists from legal trial, and in effect, from punishment; for erecting in a neighbouring province, acquired by the joint arms of Great-Britain and America, a despotism dangerous to our very existence; and for quartering soldiers upon the colonists in time of profound peace. It has also been resolved in parliament, that colonists charged with committing certain offences, shall be transported to England to be tried.”

I think this portion ultimately sums up the reasoning of at least the congress’ view on the coming hostilities:

"Our cause is just. Our union is perfect. Our internal resources are great, and, if necessary, foreign assistance is undoubtedly attainable. . . we will, in defiance of every hazard, with unabating firmness and perseverence, employ for the preservation of our liberties; being with one mind resolved to die freemen rather than to live slaves.”

But it should be noted that even this document does not necessarily proclaim any sort of independence from Great Britain, as it mainly solidifies the freedoms and liberties that the colonists claim to have been oppressed by the Crown. The early stages of the revolution was an evolving debate surrounding passive acts of disobedience and boycotting (actions such as the Boston Tea Party), versus more violent conflicts to protect the colonist’s interests (protecting the militia armories resulting in the Battles of Lexington & Concord and later Bunker Hill). Yet these actions were to be inherently not a rebellion attempting to seek sovereign independence but to assert the independence within the British empire that the colonies thought they had deserved. As you pointed out, the colonies were divided and separated not only by loyalty to the Crown but also to their own colony. Before the Continental Army was officially raised, and even a ways into its formation, the rebellious activity following Lexington and Concord was considered only a New England problem by some (or a Massachusetts problem specifically).

The Crown’s response to Congress’ continued negotiations, the Proclamation for Suppressing Rebellion and Sedition (1775), ultimately dismissed all other wants to end the impending conflicts peacefully and a clear path for war was made:

“[W]e do accordingly strictly charge and command all our Officers, as well civil as military, and all others our obedient and loyal subjects, to use their utmost endeavours to withstand and suppress such rebellion, and to disclose and make known all treasons and traitorous conspiracies which they shall know to be against us, our crown and dignity;”

And to give a bit of insight into your last question regarding the well-off founding fathers: Washington seemed intent on being a fairly endowed plantation owner for the rest of his days, but some of his interests regarding the size of his land holdings were threatened by events caused by the ongoing hostilities before his involvement in the revolution. Although this likely was not his only concern, as being a member of the Continental Congress from Virginia and the military/political conflicts he experienced during his prior service very much shaped his personal views on the matter.

All in all, I think this at least gives a surface view of some of the reasoning behind diving into an immensely disadvantaged conflict.