As a contrasting view, I'd want a bit more track real-estate as if I were planning something that I'd like to run for a while and not regret thinking longer term. I'd want at least two track loops and some area for sidings, for instance. If you have a 9 foot wide space, 30" benchwork gives you four feet inside. If that's not enough for your "butt", maybe a diet would help.
My doctor would tend to agree! On the diet, that is!