Looks like you've made alot of changes to this template.
Since you've removed the left column for product pages, does the body otherwise go across the full width of the site? I ask this because a few templates (Estorenow, Apple Zen as examples) if you turn off all columns you still have a blank column area until you do some css or other work (still haven't figured out Estorenow.)
If the body goes across full width, then part of the problem is that you don't have enough content yet to look good full width (no columns).
Try making the product image larger, probably at least 300px wide since you have full width, to see if it helps push things over. IH will eventually help with resizing imagtes.
Can you put up more text in longer sentences and paragraphs to see where it goes? Just start hitting keys, if you have to. See if it goes all the way across, which may help answer if body is truly full width.
On this layout, you might even consider turning on the right column for product pages only, where you might make some creative use with sideboxes to help fill in space.
You mean centered over the prev/next buttons? Overall, I don't know that it would look good "centered" just as it is. The left and right margins would look like something is missing? In any event, I don't know how just yet.
Text only buttons: you might be able to do this turning on the css buttons. But you'd lose other buttons you probably like.