Probably best to keep him indoors and away from other cats until he is neutered. In fact, it is probably best to keep both your cats indoors ... the dangers of the great outdoors are too numerous and unless you can provide them with a safe enclosure, then it is much better to keep them out of harm's way.
As for the difference in neutering and spaying, the techie term for neutering is actually Feline Castration - and it is exactly that. They make a tiny little incision and remove the testicles. The healing time is minimal, usually a few days to a week to remove any stitches they may have placed. It takes about a month for the "plumbing" to completely stop being functional, so even after he is neutered, keep him away from girls who may not be spayed - he can impregnant them for several weeks after his procedure.
For females, the techie term for spaying is actually feline ovariohysterectomy - they remove both the ovaries and the uterus. The incision is a little larger and it is located on the lower belly. The healing time is again about a week before the stitches (if they used them) are removed.