Hi, Z.,
I homeschooled both my daughters (now 19 and 16) all through school... who have no social problems at all (they compete on Facebook for 'who has the most friends' and they're both well over 200 of people they actually, personally know and interact with)
Check with your state laws, but many states enforce access for children outside the system to participate in sports... and perhaps there are homeschooling groups in your area that are large enough to field their own teams.
The most visible advantage of homeschooling, to me, is the opportunity for children to work exclusively (or nearly exclusively) on their strengths, instead of having to be mediocre in a whole bunch of their weaknesses... so children who are simply not going to be very social because that's who they are can concentrate on the things they will be excellent at.
Since the free market pays people for what they do well, not for mediocrity, spreading a child's energy into those areas is a huge waste of their time. I think wasting someone else's time because they're young is seriously offensive.
The transition process isn't something I've personally had to deal with - we just kept doing what we did on an average day before they reached kindergarten age... and that's what I've heard recommended: take the average day on holiday and keep going as if you're still on holiday. Later, after a period of months (some people recommend expecting one month for every year the child was in school) of decompression and relaxing out of the idea that they system has all the answers (because they clearly don't) it will become apparent that the child is developing curiosity, interest in a specific area, or hobbies/activities that use his strengths.
And really... since it's all anyone will ever succeed using, and the whole market is based on the idea of hiring others who do well what you don't do well, why would anyone spend 6 minutes of their lives trying to do things that are not natural strengths?
Take a look at the book 'How Full is Your Bucket' for a great overview of this philosophy.
Good luck! It's a fun way to live with kids...