Instant 90. What do do next?

As the title says.

I just returned to WoW after a long while and figured i'm too lazy to start the grind to 90 all over again so with the last coins left, i got myself to 90 instantly but noticed i didn't really get anything equipment wise and not enough gold to actually buy some decent starting gear from the AC.
Any suggestions on what to do first? where to start the endgame?

I would start from the pandaria quests. Take the portal from SW, do some quests until you get like 1k gold, then buy 416 ilvl gear on the wall near the honor vendor, ask somebody with double seat flying mount to take you. From there on, I guess I would do quests until I get enough gold for flying, then you can move on to shado-pan and klaxxi dailies which give a lot more gold. It would also help if you made some friends or just ask somebody on global. And a small piece of advice, do not just simply ask for gold, if you need help, explain your situation in short and then ask for a specific amount, you're more likely to get help if you're precise about what you need.