Ok, do the tank size is alright for a small number of girls - like everyone said, between 4-5 girls :)
50 watt heater is what I use - some are preset, others are adjustable. I prefer adjustable in case there is ich or something....
I have no idea about that way you mentioned of the filters... I got cheap ones usually, or made my own sponge filter and it works :)
water does not carry the beneficial bacteria... rocks, decor, live plants, filter cartridge, all do.
Some tips about sororities...
-Lots and lots of plants and decor x) silk, live and fabric plants are best, allows them to hide if needed, escape if needed, and explore of course!
-I've had better luck getting sibling girls to get along than half siblings, or unrelated bettas... BUT people have had better luck with mix girls too... Always depends on the girls :p If you want to get live plants, get a UV light... that'll also help bring out the girl's colors, along with keeping plants more healthy.
-Expect nipping and chasing!
- add them together... after floating. any time you add another fish, rearrange everything to make everyone have to scout out new territory... rather than sticking a new one into other's territory...
Breed for the breed, not for the money; the words any REAL breeder would understand.
You must know nothing in order to know all, for all is nothing and nothing is for all.