Don Y wrote:

You would also
most likely have to enjoy wobbly grout lines; the longer the course
the more difficult it is to keep spacing between tiles the same and
straight.

I was going to use the little spacers between them, fitted dry.
I can put chalk snaplines on the concrete floor to keep the
opposing CORNERS on line.

What happens to the chalk lines when you put down the thinset? Get a few
layed correctly, then use a long straight edge.

BTW, I didn't mention it but you need to mind lippage too.