Thanks for the insight and the welcome, everyone! I appreciate the tips for sure. I got in touch with a fellow to whom I'd sold an electric bass about a year ago, and he plays a Framus cutaway upright in a kind of gypsy jazz combo. I reached out to him with a couple of questions, and he said he'd be happy to give me a couple of lessons to get me started if I want. So hopefully that will help with the muscle strain...I'm sure I'm positioning my left hand incorrectly. I played violin in school, so I know good form goes a long way.
As to the action, I will tell you that it IS too high. I also play bass at my church, and this summer they bought an upright because we were doing a kind of "unplugged" format...acoustics, the upright, a stripped-down drum kit...and the action is much lower on that. So yeah, it's funny (but perfectly sensible) to think that even bowed instruments like these need a setup like their fretted cousins. And yes, the bridge is slightly warped. I'll see if I can loosen the strings and reset it a bit.
I know strings can be expensive. I was
shocked to see them going for $150 on the internet. If that's the case I'll changing strings very infrequently.

I'm sure I'll want to work up to it, but is it really that bad to use cheaper strings at first? I'm sure the strings haven't been changed in
at least 10 years.
Feral Feline, as far as style, I don't really have anything I'd like to play hardcore. I'm a multi-instrumentalist, but I learned bass before I learned guitar, so I kind of feel like that's my "roots" instrument. When I'm playing my own stuff, it's kind of a folky-tinged indie rock or alt-country. But I love jazz, old classic country, bluegrass, 50s rock...all fine applications for a DB. The string height at the nut is about what you thought it might be...that is, I can slide a credit card in there easily, but that's about it. I'll talk to my local DB friend, and maybe when he gives me a lesson he can help me make a couple of easy adjustments before I bring it to a luthier.
Other than that, I'm delighted with the bass. I love the chips and dings and buckle rash. Like you said, Greg, they tell a story. I've always been drawn to the instruments that are kind of beaters, because they're the ones that "talk" to me when I'm playing them.

I'm happy with the tone and volume.
How can I tell whether the top is carved or laminated?