I don't want to curb your enthusiasm but NPS generally are extremely demanding and a plethora of them require expert care. Many of them need almost constant feeding for survival which means your water column almost ALWAYS has food in it. This sounds simple enough until your nitrates get so high that the corals die. It seems that running a little 1.5g. pico will be simple but actually for saltwater tanks, the smaller they are, the harder they are. In a reef tank, you want your nitrates to be very low, with the best being 0. That is very difficult to do when you're constantly supplying the tank with food.
A sun coral is a good choice because you target feed vs. putting food into the water column. It's pretty awesome to feed each polyp and watch it close and digest the food (and, each polyp must be fed or that polyp will die). Have you considered some low light, soft corals? There are some very pretty ones that are relatively undemanding and don't get huge.
Again, I'm not trying to be discouraging, but I just broke my reef tank down after running it for 7-8 years and I can tell you from experience that if you cannot run a pretty-close-to-perfect system, your corals will die, especially NPS, and especially in a pico.