Help for new biker please

Hi. I am looking for a bicycle for city driving. I will ride year
round so I need a bike that can take it. I will ride in snow and
maybe I wont get to wash salt & muddy snow slop off every single day.
I am usually good about that kinda stuff most of the time.

I have a Trek 750 I found with no wheels and seat that bike shop said
to bring by and he will give me price to fix up. I just don't if bike
is correct frame size for me. I am 5'10".


So questions a
1) how do I measure frame size to see if I will fit frame?
2) Am I likely to find used parts that will fit bike at a better price
than a sed bike?

regards,
NEO