You've pretty much answered your own question. He could get your mom's dog pregnant, he probably will pee everywhere, and he probably will get territorial. I have spent years working at our local humane society, and we have had more male dogs come in for these problems than you could believe...many people didn't de-sex because they were concerned about cost, didn't want to take away their dogs' "manhood", thought about breeding someday...etc.
I certainly don't want to put down your dog, but if your dog was the kind of dog that was meant to breed, it's breeder probably would have kept it for herself. Poodles can have a variety of health issues, and you would never want to breed a dog, male or female, without ruling out every single one of them.
And, no, #2 & #3 don't have anything to do with training...they have to do with the sexual hormones running through an unaltered dogs body...if the dog chooses to spray in the house, no amount of training will stop it, ever. I have owned 4 neutered males, and never had a problem with marking...I had one that I adopted at age 7-1/2, had him neutered after adopting, and while it reduced the marking, it did not eliminate it. The faster you neuter your dog, the less likely this will occur.
If you really care about this dog, and want to be able to keep him healthy and happy, and keep your house from smelling like urine, neutering soon is the best way to go. One more thing about breeding...I understand why you feel you may want to breed him, OF COURSE he is perfect in your eyes, that's the way it should be, but if you're not showing him (and winning), he is not going to ever be worthy of breeding, and the testing neccessary prior to breeding is very expensive.
The best way to go about breeding dogs is to study everything you can, "apprentice" for a quality breeder, learn about showing dogs, (this stuff takes years), and then, purchase a dog from a responsible, proven breeder who can help you choose a dog worthy of reproducing.
For now, in a word, neuter.