If you want to make the jump to NPPL then make sure that you can afford it!!!!! Travel expenses and the cost to actually play are going to be very expensive. Dont play the league if you "just want to go pro" play for the love of the game. Its your chance to play with the best players from all over the country, so dont expect to win every game, usually your first event is more of an experience than a huge win.
Expect the unexpected!!!!!!!!!!!!!!! Pro events are usually 100 degrees or pouring down rain. Make sure that you and your gear can handle the elements and have plenty of emergency gear and lots of extra cash.
Paint is never perfect and will change a lot with the elements, so bring a squeegy on the field.
Im sure I left a lot out but I hope you get the idea.