The general rule is fish keeping is 1" of fish to 1 gal of water. Bettas are 1.5 to 2" long. However, even female bettas will fight until they figure out their pecking order, so give them more room than that and plenty of hiding spaces. Honestly, don't get more than two, and even that may be too many if one of them is a bully.
The fish are not bad together. But way to many fish for a ten gallon tank. You put one fish for every gallon. They will probly do fine but you will have to clean more.
You should only have 1 fish per gallon of water in a fish tank. I wouldn't put more than 2 or 3 Neon Tetras in a 4 gallon aquarium with 1 Betta.
Only 1. Usually a Betta is all that is kept in a 3 gallon tank
In many fish species, including bettas, males typically have longer fins, brighter colors, and a slimmer body compared to females.
Just one male betta, but you should consider a proper betta set up which can have 2 to 2.5 gallons for the one fish.
The amount of eggs they can lay at once varies.
12 to 25
Betta fish do not eat fish.
It is a misconception that betta fish do not get along with other fish. While intolerant to their own species, bettas can get along with other fish so long as they are not easy to mistake for another male betta - such as fancy guppies - or fin-nipping fish like many tetras that often go for long-finned fish. Female bettas can be housed with guppies, however.
I wouldn't put any fish in a tank that small, but if you can keep it really clean and the ammonia, nitrite, and nitrate down, a Betta is a pretty good choice
One Gallon? Only a Betta. Most anything that's small enough for a 1g is to active for one. A micro-tank can be absolutely lovely though if you plant it really well, get a rams head snail to keep waste down, and pick out a really pretty Betta.
Hundreds is typical although some will die young.