homeschool and try to meet his social needs through the local homeschooling co-ops. I need to get early admission to Kindergarten from my school district to qualify for this.
I'm not sure why you need early admission into K from the district to qualify for homeschool coops. Is it because the coop will not consider your child for admission? I'm trying to understand how it works in your state. Perhaps the coops will have your son anyway? Perhaps you could work out some sort of a parent participation agreement? Or perhaps if socialization is the key reason, you could ask the coop director if you could hang around and see if your child makes friends with other students and possibly even their younger sibs? I wouldn't completely rule out age-mates. In the beginning it was difficult for my son to find friends who were the same age but chances are there are other families homeschooling in your area for the same reasons you might...always worth a try. Necessity can drive us crazy moms pretty far (grin).
We don't have any gifted homeschooling groups locally (that I have found), but I wish we did!
Again, necessity...use it and create your own group! I've done this twice and one of them (albeit not a gifted-specific one) now counts 900+ members. You would be surprised how far desperation will drive you.
My job is to make sure he doesn't miss anything important in his self-teaching.
I hear you..."missing something important"...sigh, don't I remember that well. I assure you, he will be fine and will learn what he needs to when he needs to. You probably know that -- just wanted to offer the extra reassurance.
What are you thinking about doing for your son when he is 12 and ready for College? This question really worries me.
I joke with myself that I will homeschool till he's 12 and then unschool till he's ready for college. There's so much available to learn that I am not convinced he needs college to learn it. Not until he's craving it anyway. Right now, he wants to be homeschooled/unschooled till he's 25!
Also, what curriculum do you use?
Real life, deep discussions and lots of well-written books. And Google.

I went on a curriculum high the first 3 years and don't regret it but we don't use homeschool-specific curriculum anymore except for the one or two that are usually unschooled or if I feel I need to keep a few around for reference (that's usually when I panic about correlating what he's learning with what's expected for the age or grade level--we have some thorny asynchrony issues here).
He has been asking me for spelling help lately, so I got All About Spelling and I'm excited to use it next year. It looks fun!
Is he a natural speller? If he is, I'd suggest just reading as much as possible. Mine surpassed all of AAS' placement tests at age 5. I'm saying this to help you save some $$. Good thing with AAS is it seems to have good resale value.
PM me if you like. Take care!