I agree with jack'smom (and you) that you probably can't usefully form a concrete plan that far ahead right now. Reading and learning is good, and it seems to me that learning about all the ways to accelerate and compact won't take all that long, and then you're loaded for bear on that front. You will probably want to learn about the subject areas at each grade level, of course, and home schooling and other educational options for them, which also won't take long; that way you can be better prepared if you need to pull him out of a particular school system and home school, or go with some other non-traditional option.
Your son may be ready for all-day formal schooling earlier than 6. One aspect of home schooling him until then that may work against him is that he won't learn to fit into the school routine, while rubbing elbows with kids in a bigger classroom, so it may increase the learning curve a bit when he enters at a grade where most of the kids have learned to settle in. But it's like many similar issues with a highly able, asynchronously developing child: if he's engaged, he can probably surmount those obstacles.
If you home school until 6 and stick with the plan to enter the school system then, I'd also make sure he gets plenty of writing practice at home.
