hi Alistair. Sounds like a great project.
re mirror support, if you want to image over longish periods, would suggest a rethink of velcro - any movement of the mirror will mess up your subs. Velcro is probably fine for visual use, but my gut feeling (admittedly not backed by experience) is that it might be a bit too flexible as the scope moves around the sky.
assuming that you will be using an EQ mount, you also need to consider an all-angle edge support as well, so maybe you could consider glueing the mirror onto a ring at 0.4 of the mirror radius with three equally spaced dabs of silicon - I did that with an 8 inch f4 and it provides good stable support with no noticeable surface distortion in a very simple mount (no edge support needed). According to Mark Holm's PLOP analysis, 3 point mounting should also work fine for reasonably thick 10 inch mirrors. (
http://www.atmsite.org/contrib/Holm/...timized_cells/). What sort of mounting did you use for your 8 inch?
You dont want a permanent mounting and silicon could be removed fairly easily with a scalpel if need be (not as easily as velcro, but still possible).
I used an acid cure silicon adhesive from the local hardware store - 3 dabs about 1cm across with matchstick spacers for thickness control.
I also built a secondary holder using plastic waterpipe fittings and it works well.
regards ray