Well, we're not terribly well thought out really, MFM. 
I think we'll probably want to initiate things a reasonable amount. But no way do we intend to do 'school at home'. I think it's too restrictive, and there's no way I could be organised enough for that approach either!
We're Christians so we obviously want to teach him about the Bible and so on. And in theory we'd like to him to be able to learn about logic, philosophy and maybe Latin/classics. Basically all the things we wish we'd had chance to learn when younger.
I think really our approach is to give it a go and adjust what we do accordingly - we don't have much of a plan really. I do like the idea of working with what he's interested in. It helps that I'm a generalist and interested in everything. 
I did use to be a primary teacher which is useful in that it gives me confidence to ignore a lot of the stuff that's done by schools, or do it a different way. :)
The main constraint on how long we can HE for will probably be whether we can afford to live on DH's salary. (And I suppose that'll be affected by how many DC we end up with. Incidentally, AF has come back AT LAST after all my posting about it on the bf board so we can TTC now - woo hoo! )
The current plan is to try HE a year at a time (full time) and see how it goes and whether it works for us as a family.