Sorry Alex, but I think you are barking up
the wrong tree.
When you add Ethernet as a requirement
then you are asking for an I/O interface
that is more complex
Ethernet is cheap and trivial, drop some
code in one of these (cpu is built into the
talk ibutton on the serial port and you're done.
and more expensive
than the basic temp/hum recorder on the PIC.
Ethernet or don't bother. Serial is so last century.