If you have a veterinarian who is experienced in exotics, the neuter is a very simple and routine procedure. Anesthesia is never without risk, but the procedure is very short and often they can use gas anesthesia and it is very short acting. They usually do very well with this type of anesthesia and are only under for about 15 minutes.
I think it would benefit him to be neutered and that way you can have a companion with him if you desire.
Let me know if you have more questions,
His prostate seems full grown, will that ,make any difference?
and what gender rabbit would be best suited him?
No, it won't matter. If you get a female, wait a month after he is neutered until his hormones are gone. It might be best to get another male - but you would need to neuter him as well.
Even if you decide on a girl, you can spay her if you like. It, too, is a routine surgery for an exotic veterinarian.
I think whichever gender you prefer would suit him fine as long as he is neutered.
sorry, just one more- does it matter what age the other rabbit is? will two males be aggressive towards each other?