yes and it might take awhile but it will grow back
A Betta Fish or Siamese Fighting Fish are only a few inches. The females grow to about 2.5" and males grow to 3".
When adding fish to your fighter tank, make sure you don't purchase little 'nippy' fish. These fish will most likely start to nip at your fighters fins. They will grow back but not as nice as they were before. Some breeds not to mix with a fighter are, barbs, guppies, tetras and breeds like that. You can possibly get away with having those fish without problems if your willing to purchase a school of tetras (for example) So that they will keep themselves busy swimming around together. But generally they shouldn't really be mixed. And also when you've purchased your fish for your fighter tank make sure you let the bag float on top for at least 20 minutes so the fish can acclimatize to the water.
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
probably when they grow
Yes
When they are tiny they are impossible to sex but as they grow older the males can be easilly recognised because they develop more colour and larger fins than the females. They eventually grow into larger fish too.
Yes, of course! When they lose their scales, they always grow back!
They have special enzymes that grow it back
Algae can grow back in as soon as 5 hrs.
Depending on the damage, a fin can grow back provided the fish is cared for properly and the water is clean
Yes, but slowely.