How do I setup my fields for a tumblr-like blog
I definitely would avoid using a Matrix field to add each of these types, as they'd all belong to a single entry, which isn't what you want to do (it’d get really unwieldy, really fast!).

What you're looking to do is use different entry types in your blog settings. Each entry type can have a different field layout, so you could then switch between each.

Here’s a blog article that covers the exact thing you’re trying to do.