If you are really sure you are doing live plants and it is your first time, you are gonna meet a lot of challenges, I did. You also need to know that Ecocomplete needs the use of other fertilizers as well and root tabs. That will be a lot of money just for plant food, then add some good lights. For my sorority I have easily spent $300-400 in 6 months.
Reconsider your stocking plans again, bettas need space, the less space they have the more problems you have, max it at 6. I have 5 bettas in my 15 gallon, they love the space they have, don't cramp bettas together in one tank and expect it to work out.
Do you know how a sorority works? How you need it setup?
I am just asking these questions because it takes effort to make them happy. If you want you can PM me and we can talk more about it. You can also see my sorority in my album just to see how dense a sorority should be.
15 Gallon NPT
1g no tech bowl in the making