As long as it's a flat surface it wouldn't work on serrated tin.
Yes, although I used 2 to install and position the panes I was replacing. Allowed me to reposition with new sealant in place. Just be patient and gentle.
It probably would but most likely crack the mirror in the attempt. If the glass is directly glued to the wall, you may try a solvent, but the solvent may remove the silver backing on the mirror, again, destroying the mirror. If the mirror is mounted in a wooden frame with a wood backing, solvent may then work. The last solution if it is a valuable mirror an antique or collectors item would be to cut the wallboard around the mirror and remove it that way, take it to a professional glass and mirror place and have them remove the wallboard.
I don't think these were intended for long term placement. I clamped mine to a smooth surface and it remained there for only about two days. You might be better off with some type of adhesive backed bracket. https://www.homedepot.com/p/Command-Large-White-Utility-Hook-Value-Pack-6-Hooks-12-Strips-17003-6ES/206212338
No get a Roberts wood floor bar and hit with a hammer might need a 2nd person to stand in the area where the gap is.
This is a MFG spec question. I would not recommend it for this purpose.
No - I do not think so. Too dense with no air cavity.