Basically, stay away from fish that are significantly smaller than the betta as he may think "Yay! Dinner!", and avoid nipping fish, it's best to try some Google links and also ask the retailers, they may not provide all the information you need, but they can provide enough that you can get to a good start.
I find young cat fish about 2-4in long get along well, but beware that these fish grow large and will eat the betta once it's mouth is big enough that it'll fit.
The Betta is actually a very good community fish (as long as the aquarium is large enough), and it will get along with most other species of fish. You just cannot put two Betta males together in the same tank. the only thing that really bugs a beta is other fish with big fins, it seem's that they have a complex they need to deal with. Tetras and small catfish like bristlenose and corydoras are good tank mates for fighting fish. also you cant put female betta but you have to check that they don't beat up one another
yes betta fish have to live alone or one will kill the other.
Male betta fish are typically aggressive and territorial, so they are best kept alone in a tank to prevent fighting with other fish.
Yes it can
Any.
Some male betta fish are not as aggressive as others.
Sorry, type in: how do betta fish live?
male
Yes. Betta Fish do change their coloer every now and then. Or if you have a male, he will change his coloer if hes chaseing a female Betta Fish. Or if he sees another male Betta Fish.
She breeds with a male Betta Fish.
yes
None are recommended if the Betta is a male.
Male Betta's are solitary. They cannot be placed with other fish. That's why they are known a Japanese fighting fish. They will kill other fish for territory.