How big should it be?

[CarrotChunx]

Hello everyone!
I currently have one male albino checkered. He is a year old and is approx. 22 inches long. Right now, he is in a 10 gallon terrarium. He seems content there as he is very active, out exploring almost all day and night. Because of his activity, I want to get him into a 20 long to give him more room to move and more decorations for him to climb and hide in. However, would a 30 gallon be too large? It would be a blast to decorate and it would give him more than enough room. Would this be too much room though?
Also side question, if I were to get another snake of the same sex and species, would a 20 long be enough for the two?
Thanks!