It is really almost impossible to sex them until they are fully mature... Until last night I thought both of mine were female. Lol! Best place to get them is from a breeder, or a very good pet shop.
A ten gallon is a great home for one adult, and I fill my tank to the top, they like to swim and often will float around.
They do best with very large river stones (bigger than their heads so they can't swallow them), a bare bottom, or sand. Never anything else.
While Axolotl pellets are great, don't forget to suppliment with earthworms, blood worms, and fish (live or finely chopped lean meat fish).
And yes, they do need an air pump. Lol they have gills.