So this is the main solar collector,
just shy of one kilowatt (one square meter). Worked out pretty easy to make; just some wood, an emergency thermal blanket and a sheet of wire mesh (and quite a bit of gaffer tape, tho the next version won't rely on that so heavily).
All up about €10 and two days work, tho most of that was figuring out how best to do it.
The hotspot is significantly tighter than I was realistically hoping, about 5mm from a 50cm aperture, or 100x magnification. And that's with it not really made quite as well as it could've been, a few surface deviations and wrinkles which don't need to be there.
Still needs a clear plastic sleeve for the copper pipe, but even without gets 300 ml water boiling in under ten minutes. Whole thing weighs about 6-8kg and if I've made it right should be pretty well counterbalanced, with the parabolic focus also being the center of gravity and rotation.