Yes, your concern about China is quite correct, I think. The Chinese have very strong reasons for opposing a USA-led incursion into Iran. So it does risk expansion into a global war.

I don't know how long it would take to put out the fires in Iranian oilfields following such a war...I think 75 to 100 years is an overestimate...but it's a moot point. None of us can afford the aftereffects of a nuclear war fought over Iran.