Just a few questions on my new tank

Ok so to start with I have had my tank for about 2 months now. It's a 28 bow front. I have 25lb of live sand, 28lb of live rock and 1 clown fish in there. the light I'm running is an Aquatic Life 24" duel HO T5 fixture. I have a Rena XP1 filter on it. I also have 2x 240 gph power heads in the tank. Also I just got a RODI unit witch I haven't used yet but will be setting it up this week. Now my questions are:

what should I put into my filter?

Knowing what I know now, I would have built a sump but is there anyway I can use the filter?

Are the lights good enough to grow coral with?

I was thinking about getting REEF OCTOPUS HANG ON THE BACK 1000 OCT BH1000 protein skimmer, should I get it?

And I would like help with my fish list:
dartfish
clownfish
royal gramma
blood red fire shrimp

Is what I think I want but the guy at the LFS said no shrimp with the Gramma because it will attack it. If I shouldn't get the Gramma can you suggest something else because I really want the shrimp?

Thanks and let me know If you need anymore info about my tank