Yes, but slowely.
yes
bettas dont u sally grow more then 3 or 4 inches.
Bettas become particularly aggressive when they find other fish with large fins. This is an example of an influence in behavior. Fish can also be influenced depending on how many fish that live in the same tank. If there are little amounts of fish, they will grow quickly and large, as opposed to fish who are tightly packed in one tank, who don't grow as much and, sometimes, stuns their growth.
Yes
That depends on how extensive the damage to the tail is. So I'd evaluate the situation first. Do you have your betta in a tank with other fish? If so, he needs his own home. Bettas are loners. But the short answer to your question is yes. As long as the damage does not extend all the way to the fin base, it should grow back in a couple of months. It may not grow back with any color at first, but it should reappear eventually.
yes
bettas can't get tumors because they are fish, it is probaly just plump and healthyBettas do get tumors. Its nothing to do with them being a fish at all. All living things have the ability to grow tumors.
Yes the tail fins will eventually grow back but they will most likely not be as good as they were
2-3 inches
yes and it might take awhile but it will grow back
No they do not. Goldfish can regrow fins just as you and I can regrow hair or finger nails and also like us they can not regrow organs like eyes
2-3 inches