I’ve played this Bob the Lethargic scenario quite a few times already, but only as a refresher game without any sort of planning. I did some with this current attempt.
As to the one building guideline, I’ve done this before in part, but not on a whole city where all residential housing is adjacent to the coastline. Fortunately, the map has most of the resources easily accessible.
Played with Julius 1.60 on VH (immigration bug disabled)
No debt, no gifts, no blessings, requests met, with upgraded buildings.
I’ve listed a couple of other maps suitable for this design exercise, namely Crete (also by BTL) and the Tarraco CCK map (where luxury palaces are possible).
Here are a couple more scenarios which could make for a nice build of all coastal housing. One is Brentium by Gaius Petrius and the other is Citadell Cross by Andokai Camanis. They're both 10k maps where you can reach luxury palaces.