I skipped second grade. I'd already had subject acceleration for reading the year before -- I read with the second graders as a first grader. So the transition to third grade wasn't difficult; I already knew plenty of the kids, since I'd spent time with them the year before. That was sort of a mid-term skip; I spent about 3 weeks in second grade before getting bumped to third.
I think since your ds would be coming in from homeschooling, there's less to worry about socially. It likely won't be immediately apparent that he's a year younger, since kids grow at such different rates (both size and maturity level) anyway. Subject acceleration is good and you may need that as well, but I think I'd initially try for a full-out skip right from the get-go, and then add subject acceleration as needed.
