What trick should be next?

If you can hospital flip which is the same as the Casper flip you can most likely do harder tricks but if you mean a Casper stall that's different but try 180 ollies backside and frontside so that way when you get them down you got frontside flips an backside flips too as for the grinds you could get pallets supermarket has them and there free check in the back not in the store but like where they make deliverys it's thoses wooden squares look it up on google anyway you get like 2 and some angle iron it's thoese pecies of metal that are shaped like L's it's like 4 bucks you put that on the sides and you can grind it I've done it it works or get a flatbar