[Lumpy]

"Betas don't play with others very well at all."

This is a very good point as they really do best in their own tank. However, that wasn't the case w/ my Betta. I originally had him in a 10g w/ my African Dwarf Frogs, then my light fixture died. I said screw it and moved the Betta and Frogs to my 55g. Surprisingly, the Betta keeps to himself. I think as long as your Betta is submissive, you have a large enough tank w/ plenty of hiding spots, and no other long-flowing fin fishes in there, it can work, (IME anyway).

Bettas are also notorious for fighting other Labyrinth fishes, (those that swim to the surface for air). For instance, a Dwarf Gourami is a Labyrinth fish and is a cousin of the Betta. But, again, I had a DG in w/ my Betta, and they did fine. Unfortunately, I had to cull the DG last month due to an illness.

That's another thing to prepare for... disease. It doesn't matter if you do things "right", illnesses can attack fish, (freshwater or saltwater), at any time. Having a quarantine/hospital tank is a must in this hobby.