SDHC sizes: I think the limit is 16 gigs now, but my impression is that the sky is the limit, or more likely, your budget.

I don't think you really need more than at most two 4-gig sdhc cards, do you? SDHC cards can be damaged, and replacing them can be expensive. As in gambling, don't bet what you can't afford to lose. I went for a long time on 2 gigs total, and it was plenty for me. Now I'm up to 6 gigs total.