There is a lot of good advice here, but I don't see the social contact part. Find others who are doing the same or similar so they have to interact with their peers. My now ex-wife and I homeschooled our autistic daughter. Hard but very satisfying job. She had a very hard time with social anything but we tried. She passed the GED when she was Sixteen and had her AA by eighteen.

I taught early 17-24 year old early school leavers from 2010 to 2012, and now tutor/mentor the kids in this region who are enrolled in distance education. They come in once or twice a week to meet with a school co-ordinator, (thats not me). I just generally interact with them, and provide one on one help as needed for most subjects. I am mean, tough, sarcastic, pick on them all the time. They are not obligated to come in, and I help at their request. BUT ............... They know when I hassle them they get their work done. Kids are lazy, they like to be irresponsible, so they whinge amongst themselves that they HAVE to do their assignments and such because I make them. My foster son was the same.
My recommendation however, is if he can complete "normal" schooling, he should do so.