Hi Stephanie, I am new to this homeschooling thing as well, but I thought I'd share what I have come up with for my family. Initially I was interested in the Upstate Homeschool Co-op, as we had several friends from our church there. However, they are so full I would not have been able to get all my kids in. We decided to go with Vanguard. (I have a son going into 1st grade, as well as a son going into k4 and a son and daughter at home who are 3 and 1.) The communication with Vanguard so far has been great, and while it costs a little more than Upstate, I like that I can pick and choose the classes a little bit. The volunteer requirements were also a little more workable for me considering I have the other two at home. I know a few families with older children at Vanguard and they have been happy. It does seem like Vanguard's program is starting to grow and become more popular, so they must be doing something right. I'm excited about it and I hope its a good fit for my family.
Some other things we are doing: I'm planning on year-round school. Starting in June, in fact, So, we are doing some summer camps over the summer at the Children's Museum, and we got a membership to Roper Mountain Science Center ($35) so we can do their second Saturday's and their Friday night planetarium programs.
I'm looking into some art classes or gymnastics, etc. Something else to get them listening to someone other than me for a little bit! I'm finding there are a lot of art classes, both on a weekly basis and as a one time Saturday morning type of thing. And of course there are summer camps. I'm trying to figure what we can afford. There are several summer reading programs at the Greenville County libraries this year that your son might be interested in (the author or Pete the Cat books is coming, also some music folks and puppet/theater stuff) which are all free. Also, I'm finding a lot of programs do "after school" programs that homeschool kids can always participate in (art studios, music studios, bricks for kids). I'd like to find or start a junior lego team that my son can be on. Before staying home I was an orchestra teacher, so I'm getting my kids started on violin, and I'm hoping to maybe get some other kids together and do a little ensemble, too. Also, I found a Spanish tutor who will come to my house and work with all my kids for 45 minutes or so once per week. (I found her through WyzAnt.)
Anyway, like I said, I'm new to this. But I saw your post and figured we must be in about the same area so I thought I'd share our plans and maybe that will give you an idea or two!