Hello!
First I want to say that its great you are getting a bunny buddy! Bunnies definitely love to have a friend – I have 7 bunnies myself, and even though they do not all live in the same pen, when I put all of their ex-pens in the same area, they all seemed a lot happier, I think because they like knowing there are other bunnies around. Naturally I believe they live in herds, so that there are always some alert bunnies around to THUMP and alert everyone else if there is danger. My bunnies are not to well coordinated in that sense, they tend to all flop over and sleep at the same time and leave the herd unattended…
Waiting until after they are both spayed and neutered is a good idea for all the reasons mentioned above. In addition – if you bond them and THEN take them into surgery, you do have the complication of one possibly getting pregnant before they are both spayed and neutered. Also, you risk upsetting the bond if you separate them for spay neuter, and depending on the circumstances you might also have to keep them separated for the recovery period, and this might undo all the work you did for bonding them. So I do second (or third!) the recommendation to wait until after surgery!