You can handle them, and clean the cage, from the first day, on. It really depends on the doe's temperament, and if she is very trusting of you, then it is fine to handle them on the first day.

You should be fine handling them at the age they are now, and cleaning the cage should be no problem!

Sexing, you can try whenever you'd like. Boys when they're small, tend to have a slightly larger, and slightly further forward 'nub' and girls have a smaller, more towards the butt 'nub'.
