Web Serial Questions

Take a look at Mythic Scribes for a moment. There's a blog, and there's other pages, and then a forum.

Write a blog, but actually post your story on the other pages. Post a link in the blog to say "Hey, it's up! Here's an excerpt. Here's a link. Oh, here's a link to previous sections in case you missed them. Go read!" Do not post your story directly in a blog post. Use the blog to promote the story. I'm of a firm opinion on that one. It's all about credibility. Internet marketing is much harder than many people think it is, and these little things matter tremendously.

I would suggest updating the blog bi-weekly and your story monthly, but consistency will be more important than anything. I think that way you'll keep them hooked with your blog, give yourself a little more room for error, and the month between story updates will build suspense while giving you the chance to make sure it's ready.

Unless you're an artist, I wouldn't commit to any extras and just use them as an unannounced bonus now and then when you can manage them. Yes, though; maps, illustrations, explanations of the fantastic, bestiaries, character profiles, all of that would be a cool addition. But you need to manage expectations. Don't do it once and then stop. You need to escalate the awesomeness of your posts, so unless you can do that, start the extras small and use them sparingly.