ola saint, congrats on your new domicile.
OK, i will answer your questions in ordr to the best of my ability.
YES, if you plan on having 7.1 in this condo in the near future, go ahead and run the wire now. it will make the addition of the new speakers very easy. just mount and go.depending on the lengths of the wire run, any good 14 gauge will do fine with runs under 35 feet. thats just ballpark. if you are really concerned about it, use 12 gauge.
as far as mounting, if you use the T bracket included with the QS8's, there is VERY little space to use banana plugs. most(including me) just stick the wire in the hole. it works fine for me. the full metal brackets that axiom sells allow for the speaker to be away from the wall(so you can use the banana plugs), and it allows for you to position the speaker more accurately.. you can lean it up, or down, or angle it left or right, etc.. just more versatile than flat against the wall.. but, flat is OK to.
and as far as the unused wire on the 7.1's, if you are going to run the wires thru the wall, just leave them in the wall and put a small plug in the hole.. then when you install the speakers, pull the plug, and pull the wires out. or put a picture over the holes? use your imagination. a lot will depend on what the wife/girlfriend will allow.
hope i helped, probably not..
make sure and send some pics of the new place with your system.