Ditto to the 20 gallon long
my local petsmart has em in stock and almost always on sale
For the live plants. What has been suggested is great to start off with. For lighting do replace your bulbs with florescent blubs of atleast 6.5KW
For dividers, I know the petstores have them. here is one from petsmart
Personally, these are male bettas. So I would like to stock up the dividers with the plants to prevent them from seeing each other and stressing out too much. Some flaring is great. 24/7 flaring.....not so great.
Also, any crowntails going to be in the this tank? If so, introduce tank mates 1 at a time and when you are home 24/7. Crowntails can be VERY aggressive. Mine even attacked his plant
ETA: great idea thekoimaiden
! A lil project to do/it maybe more reliable than what the petstores sell(not sure how they stay put)
ETA2: Just saw your tank is a package deal from classifieds.