You will have to hunt for 7mm-08 ammo in some places at some times, it's best to stick with .270, .308, or .30-06, for a newbie. In addition, if you don't like hunting some ways down the road, oddball calibers are harder to sell.
The .270 is a bit light for elk, if you can't keep your range under 150 yards with it, might upgun to .308 or .30-06. Use a heavy bullet with the .270 for elk.
I hate to say this, but gun shop clerks sometimes like to push stale merchandise on the newbies, or just do them favors, in their thinking. The .308 is an excellent choice and there is no reason at all to get something else.