Yeah, that's why it's something I've been heavily debating.
The way it works now is that you can only "see" one room at a time, but everything is still connected. Each door leads to the next room, and the rooms are all arranged as part of a large floor plan. You can go back and forth between doors as you please in any direction.
I would definitely like to experiment. Since I have only built the templates for the rooms' graphics, I can go either way. I'm not restricted to doing one room at a time. The only reason not to would be if I start running into issues with C2. With the foundation I've built though, I should be okay. I always plan ahead and keep my options open.
I am going to do some tests this week and see how a larger area performs. I am probably going to design it in sections of various sizes depending on what is manageable (and what makes sense). I am also going to fire up Baldur's Gate II EE again and do some more studies of how it did level design (and how it handled pathfinding or fog and whatnot). It had levels of various sizes, some with doors, some with larger areas, and all that. After some studies, I should be able to draw up a floor plan that lets me get what I want without too much trouble.
If I can get larger areas with multiple rooms connected working, then that will be the path I take for level design. I'll just have to see what C2 lets me get away with.