I'm Singaporean Chinese, but I have an academic background in Chinese studies and culture.

The number one thing to remember with China and Chinese ethnic communities around the world is that the idea of a homogenous "Chinese culture" really only came about recently.

I'm gonna go on a quick tangent here because this is my favorite topic to talk about regarding Chinese culture. Most people don't believe it, but mainland China is one of the most linguistically and ethnically diverse countries in the world! According to this brief summary of all the dialect groups in China, there are seven language groups recognized, each of which has dozens if not more of dialects, many of which are entirely different from each other. All of these little villages, cities, and tribes have been fighting each other for thousands of years. Just personally, the differences between Chinese ethnic groups is so great that my family still has stereotypes: (Taiwanese people are snobby assholes, Cantonese people spend too much money, Northerners are tall and white and dreamy, Southerners are squat, dark-skinned, and less masculine). My family is Teochew (originating from a city near Guangdong and Fujian), and my parents always tell them to never marry a Teochew girl because they all have big noses and are ugly.

Getting back on topic, the Qing Dynasty (the last one) was Manchu both culturally and ethnically. They took over the Ming Dynasty (the last Han dynasty) and established rule in Beijing, with the Manchu homelands being seen as an ancestral land, supplying the most loyal and steadfast garrisons

The assimilation of Manchu into mainstream Han was really an assimilation of Han into Manchu culture, with mass marriages between Han Chinese officers and Manchu women occurring in 1632 ("Servants" 148).

By the time the Qing Dynasty was formally rooted in Beijing, they had brought the vast bulk of the Eight Banners army down with them. Something that was really interesting about the Manchus is that they openly embraced the culture of the previous dynasty; usually, most succeeding dynasties completely razed the buildings and palaces of the previous. Thus, much of the Imperial City of Beijing and other Ming sites are really only there due to the drive of the Qing emperors to incorporate and blend Manchu and Han culture. Fun fact, huh?

During the Boxer Rebellion, many Manchu garrisons and soldiers living in Beijing or pushed South due to fighting had already gradually lost the ability to speak Manchu, instead intermarrying with Han women and adopting their cultures. In fact, Manchu soldiers had an overwhelming influence on modern "Beijing" Mandarin. ("The Politics of Language")

By the time Sun Yat-sen overthrew the Manchus, the Chinese nationalist movement had been purposefully crafted to include all of the "Chinese race", which is where you truly see the emergence of not discrete ethnicities but one nation. The five stripes of the first Chinese Nationalist flag actually represent the five races coming under one banner: Han (red), Manchus (yellow), Hui (white), Tibet (black), and Mongol (blue) (Fossgard 2002). This unification is why Sun Yat-sen is basically seen by the George Washington of China by essentially all "Chinese" countries around the world.

By modern times, there are very few traditional Manchus alive. Many are completely enveloped in mainstream Chinese culture.

This is potentially a very broad question— one way or another, you'll be very interested in Spence's The Search for Modern China, which takes you on an overview from the tail end of the Ming dynasty through the Manchu unification and takeover, all through the Qing dynasty and up to the present. It's a great read.

Just to clarify a bit, are you mostly focused on the 16- and 1700s, when the cultural institutions of the Qing were set up? The Qing did a good job of defining China as a multi-ethnic country, but by the start of the 20th century there was some strong social-darwinist-influenced anti-Manchu sentiment, along with the idea of a China for Han Chinese only. A lot of their grievances against the Manchus go back to the original takeover, I can find some revolutionary declarations in The Search for Modern China's Documentary Sourcebook as well that are interesting.

There's a lot that could be covered under your question, from Dorgon forcing the Manchu queue (hairstyle) on all Han Chinese men in the 1600s, to the obvious 'outsider' differentiation of women in that respectable Han women bound their feet while Manchu women did not and wore tall platform shoes, to the Qianlong Emperor's action to keep Chinese influence out of the Manchu language in the 1700s... Aside from the complete shift at the very top, since the Qing left the traditional nationwide examination system intact, didn't force religious change, etc. the way of life/governance for the rest of the country remained largely unchanged. Until over the course of the 19th century a lot went wrong, but it wasn't rooted in cultural conflict between Manchus and other ethnic groups under the Qing at all.