It's natural to be nervous before your baby goes under the knife. I'm no expert as far as the BEST time to fix him, but I would think 6-7 months is ideal. That was the age recommended by our breeder & vet. And it will not drastically change his temperament, the changes will likely be between subtle and unnoticeable. It's usually an outpatient procedure, so he can come home the same day. Jackie had to limit her activity for 2 weeks, but she was spayed, which is much more invasive than neutering. So Milo should be his regular spunky self in much less time!!!
And you're right about the less complications . . . certainly there is much less risk of getting testicular cancer!