My son is older, he is 18, mild/moderate also. This trip was his graduation from high school gift! We have been to WDW about 20 times, and Disney is his favorite thing! We utilized the
DAS along with the paper fast pass system, and we rarely waited in a long line. It worked out great. Many times the fast pass return times would be 5 minutes from when we pulled the fast pass, and the standby line would be like 30 minutes! So definitely look at the fast pass return times. We used the DAS for things that had a super long wait, such as the Guardians of the Galaxy ride, Toy Story Mania, Peter Pan, the Radiator Springs Racers, etc.
He has really come a long way over the years, and I have to say, our Disney trips really bring out the best in him, he is so happy there, especially this trip. There were so many times this trip that he would speak up and ask a cast member a question about where a character would be, and he even shouted out to a random stranger that he liked her "stitch" stuffed animal. My DD and I were thinking "who is this kid?!"...he rarely talks to people he doesn't know! It was really a great experience for us! We stayed across the street at the Courtyard Theme Park hotel, so we had a short walk to the parks.