First, I think it's wonderful that you and your family are
so conscientious about your son's needs.
Many children who've been in an institutional school need a sort of decompression period when they are taken out to homeschool. This time might be one of exploration. Some people go to the library and sort of do a very gentle, loosely-structured unit study in an area of great interest to the child. It's fine even if the area isn't obviously scholarly (e.g. fixing cars, preparing Thai food, whatever). Other folks I've known have spent their first few months at home just reconnecting -- baking bread, planting seeds, going to museums, fixing skateboards, playing tennis, and reading.
I would highly recommend reading "The Teenage Liberation Handbook" as an excellent resource for adults with or without children. Grace Llewlyn specifically writes to young adults/children who have left institutionalized school for a lifestyle of learning.
Good luck and please post updates!