Maybe just do it this way: Sector A is where you start and is surrounded by Sector B,C and D. behind those sectors are Sectors E,F,G,H,I,J. then the pirate ships that spawn in Sector A are very weak. easy enough for new players. then when you head out further to Sectors B,C, and D pirates get a bit stronger then when going to Sectors E,F,G,H,I,J they will become even more stronger. but only by small bits so that you wont notice much.