[Ide]

For world size, do you want everything to be a room, or are you planning some kind of overhead view roguelike 2D map for when you're in the wasteland? That's a common mud approach to compromising between vast wilderness and time-to-build.

Dynamic descriptions are similar to static descriptions, only some words are replaced dynamically by the mud in response to the current environment (time of day, season, weather and so on) and who the looker is, what they're wearing, what their status is, etcetera.

For sheer number of rooms there are a few metrics you can go by. How many players are you shooting for? What will be the ratio of exploration/bashing/RP? Since you're doing coordinate-based it'll be a little more tricky as you'll have to finesse distances between major settlements so that it's interesting to travel between them but they're not too close that it feels constrained. You might want to consider scripted travel through 'dead zones' where nothing is built on certain ranges of coordinates, in order to control travel distance.