Similar to danimal1481, I have traveled to China and worked with people who worked there long term.
(1) For an equivalent position in the US, how does the pay in China compare for an engineer?
I didn't pry for exact numbers, but they did indicate the pay was better than here to lure people to the jobs. Couple that with a lower cost of living and they did pretty good.
(2) How do the taxes and everything work? Do you pay income tax in the US or China?
You pay taxes to China and if you're out for more than a year you don't pay US taxes. BUT make sure you talk to a tax lawyer because you do have to file special forms when working abroad. Many people have gotten into trouble for not filing the forms.
(3) I've heard that there are some perks outside of the normal pay, are any of the perks written into your contract?
Just like danimal1481 said, there are expat communities you can live in where everyone speaks English. The funny part was that I was working with Belgian and German engineers and they resented the fact that English was catered to and they had to use that as their common language.
(4) Any good or bad experiences?
Touring was really cool. My brother was over there for 2 years and he went all over the country.
As for the bad:
hygiene is a big concern, see below.
Traffic is deadly, you're going to see people killed a lot more than here.
Work safety isn't up to the same standards, if you're around construction or heavy industry, again you're going to see more severe accidents.
(5) Any recommendations for someone that is at the very beginning of his research into this?
My employer brought in a consultant that taught a 4 hour class. It was very valuable about teaching many hygiene rules. It is worse than Mexico in many ways, but when you're careful you can avoid getting sick. I managed to avoid it in 3 weeks over there. I'd google looking for a class.
I'd also recommend expat forums, again google is your friend.
(6) I've heard that some companies prefer that you don't drive anywhere. Have you found this to be a real inconvenience?
Don't even consider driving. It isn't an inconvenience at all. Find out a car service where they have an English speaking dispatcher. The drivers won't speak English, but you can communicate to the dispatcher and have them translate for you.