That would be fine for powerhead placement, you can point them at the glass, at each other, or at the rocks, basically you don't want dead spots for the detritus to settle on, either the rocks or the sandbed, you will just have to play with them after you get your tank set up.
As far as skimmers, I have used a prizm and it worked well for about a year, then it stopped working well at all (probably needs a new pump) but I upgraded to a bak-pak, and I really like it, now I am looking at upgrading again.
I think you should go with the bak-pak, for a couple of reasons, you can pick one up used for under $100, they work well, and when you upgrade to a bigger tank (more than likely you will) it can be used on a tank up to 60gal.
There are a lot of bad reviews out there on sea clones, but then there are people that do like them.