I am a crestron programmer, and from what i can tell you

what you think you will save on hardware will kill you in programming for it.

Crestron may (will) cost more but in the end, its solid hardware, and you will find all the parts needed to do that job.
Especially when you are talking critical systems like lighting and HVAC.

Hardware Advice, Crestron does make replacement switches that are wireless, and just swaps over,
same with Thermostats.

Those are easy, and givens you load level control, and fb, and its quite easy to do what you are looking to do , based on motion and photo sensors.

Ditch the lilliputs, use cheap android tablets or ipads or Itouches. They are already capactive and easier to wall mount and come will all the needed hardware, you supply power, and they work wireless. Interface for ipads and android tablets already exist for crestron, control4, amx, so in the end its less figuring and cost effective (~200 for a 7" android tablet)

Programming varies, how pretty, how functional etc...but core of it looks like 8-10 hours, and 3-4 to polish the user interface.

Just offering advice