Hi Vlad, many thanks for your reply.
I have couple USB-to-TTL adapters, but I can't get the firmware upload complete, every time the sim hangs when I try to do the upload. I decided that ATMEGA 168 isn't supported and ordered some Mini-pro 328P. The reason I stick with the mini-pro is that I have already produced the stepper slave boards (my design) and I don't want them to go to waste and wait for 3 more weeks. Lesson learned - first test the components on a breadboard and then order the PCB!
Anyway, thanks for your support, great product!