I see why you asked the size question in your other thread.
I have a 7 lber and his clothes size depends more on his girth size (circumfrance behind the front legs) and his length (measured from base of neck to base of tail). A bit of a warning, not all yorkies like or tolerate being dressed up. If Logan's previous owner dressed him up since he was little, there is a better chance he will be more accepting of clothes.
As far as food aggression goes. That is something I would suggest you seek a professional trainer for. Someone who specializes in behavioral issues (ex, NOT a Petsmart trainer). Some steps I would take meanwhile:
-definitely separate Logan from the rest of the pack during feeding time. You don't want to start his first days in a new home on a bad note.
- Ask for some basic commands before you give him his food. (Sit, down, rollover, a high five, etc.) This helps establish your role as the source of food, but someone that must be respected.