1) It will be fine.
2) Refer to the maker's instructions for clearances.
3) Yes - they have a particularly open construction, so you will need to block the passage of air in both directions. It becomes a fundamental issue when you cut holes in ceilings.
4) Nowhere near.
5) I would suggest looking at others, or canvassing opinions on makes. Personally I'm a little worried by "reflector in specular vacuum metallised plastic" - sounds like it could be a tad flimsy, and that maybe one with a metal reflector would be better.
Also, think about whether you should look for different features, or consider changing or converting the supplied ballast. Lights like that can be dimmed with the right ballast, and can be bought as, or converted to be, emergency lighting - they look just the same, all the emergency lighting stuff is in the ceiling, and they normally work just the same, the only difference is that if there's a power cut or you lose the lighting circuit they come on - can be very useful, depending where they are. I've got one just inside the kitchen above the door to the cupboard where the CU lives and two more waiting to go into the landing and the hallway.