I would do 5 girls in a tank like that, they need places to hide and places to make their own territory. I had a heavily HEAVILY planted, heated filtered and cycled 40 gal tank with 11 girls, and other community fish. And one day two of my girls started with the others and it was a blood bath. Now Thats with plenty of hiding spots and plants. Plus its best to keep an odd number of girls. If you are doing a sorority I would advise going for girls who are used to being kept together. The girls at petco/petsmart/lps usually are kept alone and once they get used to that, they get worse than the boys when it comes to agression. I have two girls left over from my sorority, and they will kill anything and everything that moves. While some of my boys are perfectly happy in community tanks and just mind their business, unless I drop shrimp in LOL FOOD!
Anyways, I would try a NPT OldFishLady knows THE MOST about that I would pm her. I have my 10 gal communtiy planted, not an NPT though. That will be my future project.
I guess my advise would be to watch out for the girls, and take your time introducing them. I really would advise against such a cramped space for 8 girls bc they will kill each other and no one wants that. Take your time and I would make sure your plants grow out before you add the girls, make sure you have tons and TONS of cover, to break up the line of sight, top middle and lower level plants. Also try to get some driftwood or anything that would create hiding places for the girls.
Keep us updated on what you do and how it goes!