Hi there, welcome
Thankfully the female is spayed, so at least you don’t need to worry about accidental pregnancies! And so glad you can rescue her!
Since you have to wait quite a while for his neutered, you might want to just set them up to be side by side, so that one isn’t too lonely and the new girl can have more interaction with you. (Only do this is if you are 100% sure she is spayed though!). The best tools for bonding are extra x-pens and NIC cubes. NIC cubes are also great for making quick temporary housing that you can disassemble and re-configure once they are bonded.
You can use the pens to divide up the free-roam space in half with a buffer (so they can’t nip each other). Since he’s free-roam, it will be good for him to start getting used to another bunny being in “HIS” area. But, be ready for litter box habits to go out the window. This would happen even if she was in the other room, as he would smell her for sure.
Once he’s neutered and hormones have had a few weeks to settle, you can start pre-bonding cage swaps, where you swap who is on which side every day or two.
.
.
.
The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.