As for breeds I would go with larger breeds. I got advice from an amazing trainer out where I live. He said larger breed just seem to connect better with his clients.
I've seen videos of smaller breeds but the larger ones can alert better and do DPT better (in my opinion).
I've seen a ton of Australian Sheperds and Border Collies and well. There aren't a ton of pitbull service dogs but there are a few on youtube.
It is very intresting the huge change in reaction I got from people. Mind you, my dog is very sweet, loves everyone, wonderful with kids. He is just a very sweet loving dog. The reaction I usually get is one of fear. Because he is a pitbull. Worse when I started on the head collar as most think it's a muzzle. There are some open to be educated and then those very closed minded ignornant people. I put a vest on him with "service dog in training" and not one person shows fear, at all. And he is very early into training. I found that to be intresting.
The one thing I did and continue to do is massive, MASSIVE research. Days upon days (full days so 8 hrs of research a day) before we started and then I spend any time I am not training learning new techniques for training certian things we are working on. Information is priceless.
What I have found is there are the positive re-enforcement, clicker/treat trainers and this is where most owner trained service dogs fall but then then are those training with remote e collar that get amazing results, add urgency to the commands, and one owner trained service dog I saw on youtube was trained this way. I did a ton of research just on e collars. The "correct way" to use it, they say, is to use the very lowest level that the dog can feel. So that is saying level 1 -100, level 1 is something they can't feel and most stopped at 5 or 6. And they also say that at the very low level, it feels like a TENS unit. I've had a TENS unit on many times and unless its up too high it doesn't hurt. They say the dog is still happy and egar to follow commands and most seemed that way. Tail up, body langauge looked eger. Etc.
So I wanted to at least give it a try (the one big mistake I made) but the most of these trainers are using is the mini educator which is EXPENSIVE and I can't pay that much so I went with the highest rated one on amazon that was in the $20 - $30 range. Also 1 - 100 levels
A level ONE hurts on my neck and underside of my arm but not on top of my arm so I thought I would try on him and he jumped across the room and yelp. Nope, that's it. No more.
It wasn't because I wanted to shock him. More I wanted him to have a slight sensation that doesn't hurt and teach him that by following commands it goes away.
To be fair I didn't use the one that cost over $100 and more in the $200 one. I just won't pay that for something I can't pre-test on my own neck first.
Also it has vibration, sound, and light. The sound he tries to get at it and the vibration I tried but he is terrified of it and shuts down on me. So it is now in the garbage.
I feel bad I did that but there are videos of both methods and these trainers getting all of these great results and many explain it etc, etc, etc. I don't think I could get that "well what if I had tried it" out of my head without trying it.
My point, use clicker and treats and praise. You will get far better results then those of 'balanced" trainers. Be careful, if you choose a trainer, as there are MANY that use the e collar to get very fast results. I saw one that said he can turn an unruly dog into a service dog in 2 weeks with an e-collar. Sure, a shut down dog doing things for you because it has no other choice. Many trainers want fast results as that means more money. I was never under the impression I could do it fast. I was thinking he would listen to me faster once he knew what the command was down pat.
I refuse to use a prong collar, and a new thing (old) thing I found last night called an q bone or q collar. Something I saw on youtube a "pressure point harness" or anything that causes him distress.
Again, I made a mistake there but wanted to throw that out there to not fall for the millons of remote/e collar videos out there. It doesn't feel like a tens unit and even those that test it on themselves use the top of their arm or fingers. I used my neck as that is where I was putting it and it seems his neck is just as sensitive as mine. It's abusive is what it is.
So now I have to work on that fear I created. He knows the sound of the treat bag and clicker clipped on the treat bag and would run to me so excited to train. Now he is a bit worried due to yesterday so I have to build his trust back up and show him training is fun again. It won't take long as he bounces back pretty easily. I do feel terrible that I did that but I wanted to warn here against it.