Thanks for your interest in STACK.
Simon and I are working hard to make the code reliable and efficient. We've been using it this term with groups of 225 students in large computer labs here in Birmingham. I'm confident now it is working well, but am also painfully aware of some minor bugs we need to fix!
Yes, questions can be served remotely. We have a "minimal client", you might like to look at this here.
This uses the opaque protocol, (as does Moodle) but does not have any content management. This is really just to demonstrate STACK is not tied to Moodle. Also, the source code of these questions is already in the STACK CVS, so they are available for use by anyone.
I've used JSMath because (i) it is a Moodle filter, and (ii) seems to work well. STACK now just leaves the LaTeX in the question. STACK could generate some MathML on the fly but the question author also needs to write some mathematics. And, we wanted to put answer boxes into equations! JSMath seems to be working well. Students very much appreciate the ability to scale the mathematics, but keep the main font size fixed. So JSMath is not a "requirement" in theory, but is the only supported mechanism currently.
I'd be happy to receive contributions from other LaTeX->screen solutions, tuned for STACK. The reason you need JSMath on the STACK server itself is for the teacher to test questions with the direct interface. If you only author yourself through Moodle, then JSMath need only be on Moodle.
If you have questions you are willing to share in STACK format, there are plenty of holes in our current coverage. We are working on 140 algebra questions to cover the material in http://www.mth.kcl.ac.uk/staff/ad_barnard/Pocket.pdf I had hoped these would be ready before term, but I just keep being ambushed with something else!
We have some partial converters for other question formats into STACK.
So, if you have lots of existing materials it may be possible to get STACK to load and partially convert them.
Thank you for your interest,