House thermostat to arduino window air conditionner controller


I'm working on building a signal relay for controlling windows air conditioner from a house thermostat. I plan to use the IR receiver on the air conditioner to activate the unit.

The Central thermostat and the air conditionner will be too far apart for the arduino controller to relay signal through IR, so I assume I would need to use bluetooth to get that range, 30 feet with walls. So probably two arduinos, one receiving the switch signal from the central thermostat and sending BT and one receiving the BT signal and sending the IR signal to the AC unit.

Central Thermostat - - - - Arduino controller(s? BT connection?) - - - - IR- - - - Window Air Conditionner.

I would seek advises for the following things to do:
1 - Design would probably be some 24VAC to 5VDC converter, was thinking using a switching regulator like MC34063 is this the most efficient way to convert the signal from the House thermostat?
2- Is bluetooth an overshoot for relaying switch signals, anything else wireless?
3- I'm also thinking about changing my thermostat to a Nest, would you think I could connect the output from this guy?
4- I would like to expand the system to two rooms. Could I use the same BT connection to send to multiple devices?

Thanks for your input