I like the idea of the filstar. It's like a sump, but closed
I might consider it for a little 2.5 gallon pico tank I've been thinking contemplating. Could double it's water volume, potentially.
Is that your final decision on lighting, or are you going to get those coralife crappylight minis? I bought two for a nano I used to run, and they were utterly disheartening. They couldn't reach any further than 8" without losing most of their PAR.
The light you have on it now seems pretty good. And it hanging off the sides isn't too bad, considering a MH setup would have WAY more overshooting of light than what you have now.