@Jerry: the AC just removes chemicals from the water, but doesn't play any part in actually filtering bacteria/viruses in the water. I was following Ike Mouser's thread about using household bleach (sodium hypochlorite) and then using the AC to improve taste and remove the chlorine.
For my question #2 above: I should have read a little bit more. It turns out the MSR Sweetwater Purifier liquid is a 3.5% sodium hypochlorite solution, not chlorine dioxide. Basically, household bleach. I think that Klearwater is the only pre-mixed chlorine dioxide solution on the market (something I've never used and can't comment on).
Btw, there is some noise on other threads right now about pre-mixing AM liquid before a trip, how much to use in different parts of the country/with different water sources, etc. For me, more than anything, this is just my latest "gear distraction" and whether I'll actually use any of it remains to be seen! It is fun learning and playing around with new stuff!