Good that you separated them – as said here, leave at least 2 inches between cages also. They can get to each other through the bars. And if one is out, don’t let him/her go up to the other one during play time because they can touch through the bars then too.
Wait a minimum of 4 weeks after one (his neuter) gets fixed. His hormones may surge briefly during that time before finally calming down and no longer a risk for pregnancy. After that you can begin the bonding process. They should get along fine, but baby siblings and friends often don’t remember their bond, so proceed as discussed in the Info. section for bonding on the site.
Don’t forget to plan to get her spayed as well. The females need it to prevent cancer which is painful and expensive later on, so you would do her a great service to have her done, too. His is cheaper because it’s easier. And also usually can be done sooner. If you look in the Q&A section BB has posted lists of sites where you can find recommended vets in your area. If you don’t like your vet, the price or the waiting time, you might find a more experienced vet near you that can do it sooner, or is more comfortable with females so you could have her done first. Both bunnies behavior will benefit from it as well. (Less aggressive, easier to bond.)