Ditto on the life expectency related to temperature. My bettas in
heated, 75 degree tanks, lived about 2 years from when I hatched them
from eggs. My girlfriend's, who were all in an unheated 10 gallon
tank, are all still alive. The mom of the bettas is now in her 4th
year in a 1 gallon unheated tank (68F/20C) and still quite active and
healthy. She's been fed only four betta pellets per day for most of
her life, which at first I thought was too little, but who am I to say
since hers has outlived most of my current fish.

Keep them separate and unheated for longer life. I personally think
they are fine in cups for short periods of time (ie. in a fish store),
and the liveliness and longevity of my gf's is testiment that smallish
1 gallon tanks are fine.

I keep females in a community tank now, and the hardest part is keeping
the other fish from stealing their pellets (which is a problem, since
my bettas don't eat flakes; only pellets).

tim