Hello, and thanks for this theme, which I really like.
One question, though … is it possible to put regular text in the header [as site-title], or does it have to be a graphic?
You can remove the logo on Frontier Options. You can also disable the whole header if you want. The site title and description is already available on the top bar but if you choose to disable that and want to put it on the header you can put your site title text on a text widget then place it on the Header Widget Area.
You can enable widget areas on Frontier Options -> Widgets