For those who read the other post, I dropped the recessed wall heaters
idea.

I am planning an addition where I would indstall two plain 4 ft.
electric baseboard heaters controlled by their own thermostat (one
thermostat for both). The rest of the house has hot water radiators. I
figured I would by two 750W 3' units from QMark or Comet (the room is a
little over 100 sq. ft.)

First, I am wondering what the big difference is between 120V vs. 240V
(beside the obvious). What would make me pick one over the other?

I am also having a hard time figuring out the wiring. On the wall, I
should have one wire going to the unit #1 and one wire down to the
basement. Do I need a relay box of some kind down there? I was also
gonna put both units on one breaker, daisy chained together if you
will. Is that a bad plan?

Since we're contracting the work out ourselves, I am trying to be as
prepared as possible when the electrician comes by to quote me on the
work.

Thanks.