I would like to buy a second garter. I currently have 1 male red-sided garter.
I don't have very much room for another 20gal tank.
That makes me think it would be easier to just put him in with my other snake.
It would be hard for me just go and buy a second tank, whether it's for a second snake or for quarantine, but I will if I need too.
As for quarantine:
1. Is it necessary?
2. How big would the quarantine tank have to be?
3. How long would I have to quarantine?

And if you can handle it, are there any snakes that should NOT be in the same tank with my other snake(red sided)?

Sorry. That was a lot of stuff to answer...