You can keep your little guy in anything 2.5 gallons or larger ;)
Definitely get a heater(bettas need a steady temp of 78-81 degress F), you don't necessarily NEED a filter....but if you want to go 5 gallons or larger, I'd suggest looking into cycling
, and you'll need a filter for that.
Water changes are determined by how large your tank is and if its cycled or not..
In a smaller tank(5 gallons or less)you'll want to do 2-3 100% changes per week(though you could get away with 1-2 in a 5)/ Just used hot water and rinse everything, NO soap. Its toxic.
Be sure to match the new water temp with the old water temp, add water conditioner to the fresh water, and then add your guy back in.
Good luck in finding the right home for Jack ;) There are some really neat tanks out there to choose from!