A is the default slot that all powers come with. The (5) represent the 2 slots you get at that level. The enhancement in there is not one you can get until much higher level, so for now you fill it with anything.
Most of the enhancements are IO's, which have set bonuses. You won't have these at first, and they really aren't worth worrying about until the 20's at the earliest.
Most of these builds look significantly different while leveling, and even at 50 they look different unless you have ridiculous funds. In other words, a great build that costs 10 billion influence looks different from a very solid build that only uses 100 million.