I would be very careful in doing this plan. I understand the wait for an autism assist dog is huge, it's over 2yrs at the organization I work for (although many place for free). But keep in mind that there is also a high drop out rate for service dogs and organizations have already weeded out those dogs for you. Plus they will be able to provide you with the support you need in working with the dog and your child as a team.
Service dogs, for any type of work, have to BOMB PROOF. They have to be very relaxed out in public and able to handle all sorts of things. You will be shocked at the number of people who will try and poke your dog in public, kids who run up to it waving bats, all sorts of noises, different floorings, people in costumes, and the list goes on and on. The plain truth is your average pet dog can not handle the stress of going out in public and dealing with crazy crowds.
For an autism dog they not only have to be able to deal with the craziness of those public outings but also be completely calm in the face of an autistic child's tantrums. Many dogs will tolerate children but most dogs WILL get freaked out by little kids running by and screaming, let alone a full blown tantrum.
If you say you are in school full time how will you have the time to care and train the dog? Keep in mind that while you are getting a working dog you also need to remember that it is still a dog and needs exercise and mental stimulation. How will you exercise it on a daily basis?
None of what I said above is meant to offend you in any way. I just want to make sure that you are fully aware of the type of dog that is needed for service dog work.
If you do decide to get your own dog I highly recommend taking a professional trainer with you to the shelter/breeder and pick out the dog. I also recommend that the dog already be 1-2yrs old so that you know what you are getting in terms of temperament. Be VERY picky in who you are choosing.
Then, you will need to invest a lot of time in basic obedience and I strongly advise that you work towards the minimum standards in the ADI public access test:
http://www.assistancedogsinternational.org/publicaccesstest.php
Good luck!