Matt, there's a guy here in Portland who does essentially what you are doing. He had all his inventory indoors, and he dealt mostly BMW's with the occasional Porsche, Merc or LandRover plus whatever trade in he might take...
Business has been good for him, he relocated to a larger space; I check his inventory from time to time, and stuff seems to move. (Stuff always seems pretty high to me, too, but I guess you need some wiggle room)
(BTW, he is just a super nice guy, no hint of a used car salesman in his persona.)
Good Luck in this endeavor. I'd buy a car from you, if the need arose!
He maintains a simple website...
http://www.stanbennettsales.com/index.htm