Wherever you plan on putting the shack remember this, power, ethernet, phone, etc etc...
Pre-run everything in the walls!! And since your starting fresh have them run network cable to all the rooms of the house to plan for future needs and have a panel in the basement where it all terminates, pretty standard now days for new construction to plan for these needs. Also cable tv runs, phone line runs, etc etc.. And speaker wiring in the family room or even a dedicated media room, get all that stuff in the walls even if you don't need it right away!
Going back to the shack specifically, think power. I ran two dedicated 110v 20a circuits to the shack, and i still might have to run a 220v line in there for future use. It's nice to have lots of outlets without a bunch of power strips and such. I have three two gang boxes under the operating position alone, thats 12 places to plug in!