You can start with 1000 but be very carefull. Use running warm water , not a bucket ,to keep dirt out of paint. If you have dirt in your water or hose rap a paint filter on the hose to filter it. You will notice when the sand paper looses its bite, it dont take long ,get a new piece, buy a lot of paper as it will save you time.
Use a rubber squeegy in good light to see if the peel is gone then go to 2000 and do it again, then 3000 if your going for that deep shine. depending on how many coats you have on. You dont have to rub hard, let the paper do the work. Use a block or paint stick to sand as this will smooth out the paint. If you use your hand or fingers you wont be happy as you will see all your finger marks when you buff.
Dont sand the edges directly , sand toward the edge and over keeping the stick on the flat panel, dont pull back, then on the other side of the edge do the same thing. This will keep the edges and lines straight without sand throughs.
DONT RUSH IT, Take your time, you will be glad you did.