Wow thanks again, expect Cricket PCBs in the mail.
Now the schematic and testing are 99.9% done (I'll post the revised schematic on my site), it's on to the layout. Same size as the Inchworm, Firefly & Dragonfly PCBs 107mm x 57mm (Hammond 1591B case)
Design thoughts, the Cricket needs to generate as little of its own heat as possible. Slow running PIC, latching relay, low baud rates, LCD display, parts location (the LM34 is in the lower left of the PCB)
There is a provision for 3xAA Alkaline for running during power fail (or running sans RS485)
So the problem is the main power source.
A 5V switch mode wall wart (they are cheap now) this is the least expensive route and will keep the kit price down
A LM2575 or other low power switching regulator (can handle up to 40V so 24VAC HVAC can be bridged on to it) $$
A "Roman Black" switching 5V supply (not tested)