Under Armour Men's 2.0 Base Layer Leggings (Regular and Big & Tall)

These just come by normal size letters s,m,l,xl,2xl,3xl but they have on their website a sizing chart to use as a cross reference for inseams and waist fits. I suggest from my experience that use your waist size and inseam to cross check there size recommendation. Example for me i have larger thighs so sometimes i use a size up to get proper quad fit and will be a little looser in the waist but works well for me , Everyone is different so the sizing chart helps , One other important thing to remember is to always check the cut or fit type which makes a major difference in properly fitting and sizing such as Loose fit , Compression fit in the same size like a XL are both different fits so just to remember when your selecting your garments

They have a nice insulation lining inside but from my experiences in those low temperatures i would suggest tights and tops made with cold gear they are excellent and designed for extremely cold temperatures

Yes , they have style with or without front fly flap opening I purchased these because I wear Lightweight Shorts over top of the tights and they are cheaper than tights with no front fly flap. It was my preference for what i was doing.

In my non expert northern opinion, with a pair of coveralls or jeans these would be sufficient for those temps. Probably more for the low end. Mid 50's if youre working might be too warm.

I think you would be fine with the 2.0 and save a little bit of money. I wore these under uniform pants and gortex bottoms for the water proof and shoveled for almost half a day and was sweating. Not quite the same outdoor activity but I would guess you would stay warm all day snowboarding.