Well, I would recommend getting a nice quality juvenile from a breeder...

Personally I would recommend a 10 gallon for 1 male OR a few females. Optionally you could setup a divide in there and keep two males.

Make sure the tank is heated and has decent filtration.

Feeding should be varied, but healthy. Pellets, and mix up a bit too, like blood worms etc.

I'm sure Rose (Chicakdee) will come in too and fill you on in all the details too, she is the "betta expert" round these parts.

Good luck,
tim