So I imported a large object (geometry) that I made in blender, and it was much taller than I expected. I can't zoom back to the origin now, because the zoom steps are huge, and I can only zoom in increments of about 5000. How can I zoom in to the origin now, say into a 10x10 grid?

You can reset the view dolly to show everything using Space+A or Space+H (or Alt+A / Alt+H, or just A or H if you're in view mode). A just resets the dolly of the view (how far back the camera is), whereas H resets the dolly and the angle of the view. You can also hold Shift while using the scroll wheel to dolly slower; (if you're not in view mode, you'll also need to hold either Space or Alt while scrolling). Hopefully one of those helps.

I actually don't know what the hotkeys are for doing true zooming, (i.e. reducing the field of view angle of the camera), because that's something that I don't want to risk changing by accident; I tend to change the Aperture parameter manually on a camera in the cases when I want to adjust true zoom.