Not used to this code so it will take me time to figure it out. I have only had a few hours to play with it and already starting to understand it. (BTW my errors trying to compile your revision on svn was caused by my internet.) I have now done simple things like change hard codes and recompile a working version but when i scripted the starting rooms and room cost to CFG it crashed. I will keep trying.
Good-oh. Give me a shout if I can explain anything.
Change default number rooms and cost to add rooms in CFG. ( I believe I found everything in cBuilding.h and cBuilding.cpp. Need to alter cScreenBuildingManagement.h and cScreenBuildingManagement.cpp so new prices will show properly.)
Sounds good to me.
Change the default number of interactions allowed per week. Current Default 10. (Haven't found this code yet.)
It's a global: g_TalkCount. Defined in InterfaceProcesses.cpp, checked in cScreenGirlDetails.cpp. It'd be worth adding this to the config file as well. We've had requests to reduce the number of interactions possible, as well as to raise it, so a config file entry will probably generate the least controversy

These are the two things I want to first tackle and see if i can adjust them. I hope I can be of help as the code doesn't seem much harder to understand then code for many multiplayer games I modded. Just different.
I'm glad you find it fairly clear. Like I say, give me a shout if you get stuck.