Using Apple Watch without cellular and wifi

At work I find that I can get quite far from my iPhone and the watch still seems to be able to be able to connect with it. This despite the building being predominantly concrete and steel. Being an Amateur Radio Operator, I know that concrete and steel can severely degrade wifi signals. But I seem to get better response than I would expect. My point is that you may have pretty good results even from greater distances, just don't count on it.

The GPS only Apple Watch can do  Everything  the cellular model can do  as long as  your iPhone is  nearby, where nearby is somewhere in the same 3-4 bedroom home (assuming typical wood frame construction).

Yes. It’ll use the data from your iPhone.