More or less the same recomendations as for your other map.
Texture resolution, better lighting, more detail.
Allthough i'm not sure if you can do much more about optimisation without alternations to the map layout.
As fror your questions:
1. no you cannot force a certain gameplay only for certain maps.
ofc. you can force your server to run only certain gamemodes, but that will apply to all maps.
Also other server owners that run the map have other server setups.
So it's the job of the mapper to make maps compatible with gamemodes.
2. have you tried adding an item_armorvest entity?
3. the menue thumbs are located in ...gesource/materials/VGUI/maps/
but if ppl don't have the map and download it from the server, they won't have the thumbnail anyway even if it's downloaded as well via .res file.
Who uses the map list anyway? It doesn't show all servers.
I'd rather invest the time creating a loading screen since more ppl will see this (allthough the same applies here, no screen on downloading the map, only if it's played again after downloading).
