Thanx for your feedback!
I have also 12V power adapter but it is connected to 5V switching regulator (5V linear regulator 7805 got too hot and heatsink took lots of space) and with this 5V I power Nano and ethernet module and for radio is separate 3,3V linear regulator powered from 12V.
Everything is cool exept ethenet module chip and module 3,3V regulator.
I waited a day but no communication between Nano and ethernet module (all lights are blinking) and no ping reply. I also uploaded simple web server sketch but web server also not working.
First step is ordering one cheap w5100 module from China. And also check things with oscilloscope.
Probably I must take a time and test ENC based ethernet module with Mega and softSPI. And if this combination not working or working but not reliable then old good serial port is last resort.
But openHAB will not have serial binding for mysensors what mean that I have to look to another controller or make my own controller.