Service dog?

   Hi. I am considering training my dog to be a service dog and would like some help in making my decision. First of all I just want to say I know that no one can make the decision for me, and that it is a serious matter to be considered heavily before making a decision. I just thought that it might be a good idea to post something explaining my situation so that I might receive some advice, or in case someone makes a point I hadn't thought of yet. This is a big decision and I want to know as much about it as possible so that I make a good choice. This is a decision I will also be discussing with me family and my psychologist. But I thought that speaking with others with autism might be beneficial (I am also using forums about service dogs).
   So getting to my situation. I am a young adult with autism and a generalized anxiety disorder. I am beginning to become more independent, I'm about to start college and I take myself to some of my doctors appointments. The problem is that my sensory issues combined with my anxiety prevent me from doing a lot of things I should/need to be able to do. I cannot go to the grocery store by myself as the bright lights, loud noises, and stressors of trying to stay in budget raise my stress so high I have to leave the store prematurely and usually have a meltdown in the car (in the parking lot) or the second I get home.
   I also cannot do things like go into a restaurant, even a fast food one, I am only just comfortable with using the drive through (and I am not comfortable eating as I drive). Since my appointments are in the afternoon and an hour away from home this often means skipping lunch entirely or eating hurriedly in the parking lot. There is only one store I always feel comfortable going into by myself (a craft store that is usually not crowded or loud), and on a really really good day I may be able to go to the library as well. When I have to drive myself to a doctors appointment by the time I have gotten back home I am too exhausted to do anything the rest of the day and sometimes can't do anything the next day.
   My dog will come over to me when I'm stressed and having a meltdown or on the edge of one and roll over so I rub her chest in a circular motion (an action that is extremely calming for me), or let me rub her soft furry ears (sensory heaven). She even sits in my lap or on my foot (if I'm standing), something she normally doesn't do or enjoy. If she cannot calm me down or I don't begin to pet her she will go get my mother so that my mom will calm me down. I think I could also train her to bark or paw at me until I stop doing self harming behaviors (hair pulling, hitting my head, biting my wrists, or scratching aggressively at my arms). This would be useful because when I am calm I know I shouldn't do these things. But when I'm stressed or having a meltdown I cannot go through the thought process of 'this is bad for me I need to stop'. I think she could also be trained to remind me to take my medication (I often forget) but that is not my main goal.
   I believe having her with me would keep my calm enough to allow me to do things like go grocery shopping, get food, and take myself to important appointments without leaving me ill. I obviously wouldn't take her with me unnecessarily. I wouldn't take her with me if my mother or another trusted human companion was going with me who could keep me calm. I wanted people's opinion on this because I really respect the laws and system that allow people to have dogs who help them function with them - and I don't want to be taking advantage of this system. Once again I know I am responsible for the final decision on this, but I wanted to gather as much relevant information on this as possible. If you have any questions that will allow you to answer better I will answer them as well as I can. Thank you for reading this (I know it was really long), and for your answers, I really appreciate your help.