I would definitely not factor in "lugging stuff back to the room" in selecting a pack. Most stores still offer plastic sacks, which you'll find uses for along the way anyway. Or just bring your own very light plastic sack if concerned.

In terms of resupplying on the AT in particular, it's by far the easiest of the "big three"; thru-hikers typically carry just 2 - 4 days of food on that trail as resupply options are so frequent. When I hiked the AT in 2010 I had just 5 resupply boxes for the whole trail, and that was plenty (mostly to send myself new shoes and prescription med's).

I'm not saying that you're "wrong" to do it another way. Most folks, however, who start out with the idea of sending lots of boxes end up regretting it. I certainly learned my lesson on this the hard way, and fortunately dialed it in right (for me, anyway) for the AT.

I'll be hiking about a month on the AT starting in mid-March, and plan on one resupply box at Fontana Dam (NC) just because my recollection was that it was somewhat of a hit-or-miss PITA to resupply there, depending I think on lodging options.