Electric motor load

I have been lurking around this forum for the past month or so, and I have found it extremely helpful. I now have need to post a question of my own, I apologize if it has been addressed and I did not find the respective post. I own a 1956 Cape Cod, and I currently am rewiring a couple of the original circuits so that they may be grounded. I am also remodelling the main floor bathroom. In opening up the walls, I found that the GFCI receptacle in the bathroom was on the same 15 amp circuit as several lights and the receptacles for a bedroom. I will be running a separate 20 amp circuit to serve this bathroom (I have several 20 amp breakers in my box that are unused), but I do have a couple of questions concerning what it may serve. 1) Directly below this bathroom, I have another bathroom in the basement that does not have a receptacle at all. If I decide to run a 20 amp circuit to this basement bathroom to serve a GFCI, can I run this circuit to the main floor bathroom? 2) In the main bathroom, I also have a switched fan and a switched light (separate fixtures). Should I run these off the GFCI, or should I continue to run these off the current 15 amp circuit? Thank you in advance for your words of advice.

I am finishing my basement to add a family room, bedroom, bathroom and den. I plan to heat the FR, BR and den with electric baseboard heaters. The family room will have two 1500 Watt heaters, the bedroom and den will each have one 1500 watt heater. I would like each room to have it's own thermostat. Can I do this on one 30 amp 240 volt circuit? I know the wattage would fit on that size circuit but how do I continue the circuit from one room to another keeping in mind that a separate thermostat controls each room? And what is the difference between single and double post thermostats? Thanks!!