Sounds like a good deal.

If you go the blog route, you can host the thumbs on your hosting and store the full pics on an image host like http://imagevenue.com/, if you're going to do your own galleries. If you intend to use the free hosted galleries provided by most sponsors, you don't even need that -- you hotlink the thumbs provided and link them to the gallery page.

All this means that you can make do with 5GB/month bandwidth just fine, unless your blog suddenly becomes THE most popular smut site in the world, which is unlikely.