Exactly. ~90% of Iran's crude went to China. The oil revenue was ~75% of Iran's budget. Iran has been a significant area of military development for China, serving somewhat as a forward base.
That doesn't exactly limit the impact of cutting off the supply. It's a global trade market. If China buys on the global market from other places instead of Iran because that oil isn't available, that still creates a shortage for everyone and that still pushes up the price of oil for everyone.
However... higher oil prices also increase energy prices across the board, and China's energy sector is dominant in renewables. I think they're more than happy to have the competing energy sources become even more expensive.
Maybe? I wouldn't count on it. The US may be a net petro exporter, but it's about 1% of GDP. The other 99% are not going to do well with inflated energy prices. So exports might net go down.