You can stop your dog reproducing without having it neutered. I have managed to keep entire bitches for years without an accidental pregnancy, as have most of my friends, including those who keep dogs and biches (not all have entire dogs, but I don't know of one accidental pregnancy amongst people I know). However, obviously neutering means it definitely cannot reproduce and there can be no 'accidents'. Responsible ownership does the same however.
It might stop the humping, it might not, but the humping is behavioural and can be stopped if treated as such.
Weight can be easily controlled by diet and exercise.
I'm not going to go into the other pros and cons except to say, there are less cons if you wait until he is fully mature (assuming he doesn't have a retained tescticle?). Have a look around the net for info on the pros and cons of neutering, especially early neutering and discuss fully with your vet, armed with whatever info you have found. Vets are very good at not mentioning the cons, one lady on here very sadly lost her dog during neutering surgery, something that sis very rare, but that her vet had not mentioned to her was a possibility. 
I have an dog here, just over a year old, who is not yet neutered. He will not be neutered until fully grown (about 2 in his case) for various reasons, despite the fact that him not being neutered makes my life very difficult as I have three entire bitches in the same house, who all usually come into season at different times, including one who has 'silent seasons' and obviously he must be absolutely kept apart from them when they are in season.