I guess it's not too important to regulate the temperature if you're just dehydrating simple foods.  You can upgrade to a Nesco though, they aren't really very expensive.  I recommend buying a ton of expansion trays for it though, if you're going to work with cactus at all.

I'd start the cubes on the side, kind of like hedging your investment.  If I could, I would, but I can't do anything out in the open.  Well, without getting complicated with the setup, which I'd rather not do. (Some elaborate ninja camouflaged deal, looks like way too much work, and would probably still stand out here anyway.)

Yes, fruiting my leftover substrate is the next step.  Got it all planned out, how to do it from beginning to end.  Just haven't gotten to that step yet.  Currently my Mex A leftovers are sitting in a bucket, which I'm watching curiously to see what they do.