Some vets are quite happy to do neuters at 4 months old, so it might be worth looking around.

I don’t recommend doing any bonding work beforehand. At his age, he will just want to mount the younger bunny and she will be stressed. You don’t get a true bond happening when they are this young.

No, you cannot put them together until they are both fixed. Even if he is neutered, his sperm can remain viable for up to one month or longer, so as a general rule I believe you should wait at least a month. I understand she is not going to be sexually mature at 10 weeks, but she will be soon enough, and when she is she will be territorial and it is highly likely that they will begin to fight. They can seriously injure or even kill each other. Also, if they are fighting it will be more difficult to bond them after they are both fixed, because they do not trust each other. As a general rule, rabbits cannot be bonded before they are both neutered/spayed. I suggest keeping them completely separate until both have been fixed and are recovered. Bonding is a slow process, so don’t try to rush it. I have a 6 month old female that is spayed and an 8 week old male that has not been neutered. I am keeping them in separate rooms. You need to keep them separated for their own sake.