well when angels get bigger they will probably end up eating the neons. with that said i have my tank over stocked and have 6 angels, a breeding pair, i belive another female and 3 other males. along with 15 columbian tetras. way to much for the tank the angels are smaller in size but do breed have layed eggs 5 times now but i have not messed with trying to save them. and the tetras out compete the angels for food so i think that is also a reason for their small size. i would say go with 4 but if you want a breeding pair or so in a 55 get more and when some pair up you can always sell the others.
newest pic i have of the tank, when my pair lays eggs they end up running every one out of 1/3 the side by the filter (right side in pic) and lay on the big sword leaves i have had these angels since oct of 2011 and they were about 6 months old when i got them they started laying eggs around oct 2012 and have had 5 spawns now but i dont have room to raise babies so i ony have one angel fry atm