Enough for them to believe that they live in a democracy, it seems (and I don't say that sarcastically).

It's not like people in liberal democracies have more influence. We can't choose who runs, and each individual's vote is negligible. I don't know the specifics of China's government, but I suspect they value being able to influence local policy and higher official elections via the Communist Party more than a direct vote on its leader -- I would too, honestly.

A fair bit, actually. China's political system is basically a popularity system from bottom to top. At the lowest level, politicians only stay in power if their population is happy. This trickles up to the provincial level, where politicians again only stay in power if their population is happy. At a national level, the national leaders stay in power by building, essentially, large cabinets out of different provincial and regional leaders - thus, their entire position relies on keeping the provinces happy.

It's not the perfect system, but Chinese citizens can fairly easily impact local and even provincial policy and, by extension, influence national policy (recently, by repealing the COVID lockdowns with mass protests).

The CCP isn't an absolute monarchy or something. At the end of the day, it serves it's people. The power of the Chinese economy is in its industrial capacity, after all, not in its wealth: the needs of the people need to be addressed to keep the country stable.

The same as the average western person.. So probably very little.