This is something I discuss in my economic development series; I would actually split the fleet and the shipyard between the new city of Salt Harbor and Barrowton. This way, you:
- Spread out the benefits of economic development to reach more of the North.
- Spread out the largesse of House Stark so as to keep as many houses as possible happy, and to keep any one house from becoming too powerful.
- In war, make it a bit more difficult to pull off the Moat Cailin strategy by using the fleet and boom chain at Salt Harbor to guard Barrowton’s shipyards while said yards keep the fleet at Salt Harbor repaired and reinforced.