Re: Few beginner questions
Welcome to the board!
Most leucomelas and tinctorius are good "beginner" darts, but the leucs certainly have a loud call.
Tinctorius are generally not audible outside of their tank, so they would be great for you. As for what morph, just pick the one you like the looks of most, their care is very similar across the board.
I would use the 20G for a pair, setting it up horizontally (conventional) as opposed to vertical like you would for many of the climbing species.