I have a FInnex four gal and I hope I am not too late on this suggestion. For more light I just went and bought one of those Home Depot $20 lamps. I use it along with the 13 W light that came witht the finnex and I can grow anything, I was finally able to grow HC. Once I got the HD lamp on there THe HC took off in a couple of weeks. I highly recommend them. I have since removed the 13 w light and know I just use the HD light.
You can also look at the Ott lightes that Ugly Genius uses, you would have to contact him about the specs though as I have not used them but they look great on his tanks.
As far as fish I used to have a dwarf puffer fish in mine, Just one though. He/she was very comfortable until my DIY CO2 system back up into the tank and the PH levels raised too much for him. he wasnt the same after that and died a few weeks later. (I have pressurized now). Now I have 8 Rasboras Briggatae in there along with 12 tiger shrimp and it always activity going on. Its quite fun to watch now. The Rasboras are very small and I think the perfect size for this size of tank. I got mines from Pedro on this forum.
I hope I helped, And I cant to wait to finally get to see some pics, already.
EDIT: We really Finnex owners really need to get the Finnex tank club going, I think I see a new Finnex four gal every month on this forum. LOL