How many angel fish?

i have a tropical aquarium with some fish in(i have had heavy lossed thanks to ich and ick, and small fish getting into the filter, and other reasons) so my 15 gall aquarium is not fully stocked,i have a few pepper corys and platies , but they dint take much space,so i have decided on a single marbled angel, i have heard 2-5 will fight for dominance and have been told to get 6+ or a mated pair, but if they grow fast they may outgrow the tank i have, the shops sells them on offer for 4 for �16 or �5 each(these are small angels) the big ones are about �30, so should i get a single angel, or would it get lonely and ill, would 4 very small be ok in a 15-17gall aquarium, i would move them to a 30-50gall when they reach full size probally(if i have enough money im only 15 :P) so would that be a good childhood home for them? its densly plated with hiding spaces so stress wont be a problem, i have been told yes and i have been told i shouldnt. i need more info and quick,im going tomorrow.