Question a. Are big temp swings happening dynamically in 1 week or statically over weeks or months? Temp swings primarily mean drastic changes in humidity, while expansion and contraction happens it's primary going to come into play when in the same week or over a span of weeks you have huge swings of humidity, for example Houston in the fall/spring where between 1 week you have humidtiy of 70%, 20%, 30%, 90%, and 10%. If they happen slowly across seasons you may not need to factor in as you are.

1.Concrete can carry moisture and you don't want this moisture to go into your wood studs especially during humid seasons or wet/rainy/monsoon seasons. You can circumvent this by getting treated 2x4s, 1x4 or whatever size wood you decide to frame with. Otherwise you can do literally any of the options you described, pink boards, vapor barrier, or offset from wall so only bottom piece needs to be treated wood. You could also put the 2x4 on a vapor barrier on the ground and then you wouldnt need any treated wood.

2. It sounds like you are saying (i'm deciding randomly) that your north, east and south walls are outer facing and your western wall isn't and so you want to only frame these three. No risks to doing this. Insulation is used (framing and drywall included) are done to prevent sound, temp, and motion transfer. in your situation you would be insulating from sound and temp since these aren't load bearing walls. You would do this wear you want to prevent sound and temp from transferring for any reason.

3. No reason to vapor the floor except as mentioned above. If you have lived in the house for a while and are pretty sure there aren't water issues in the basement then no real reason to do beyond what you already did, which is a moisture test. That being said your primary concern having a woodshop should be airflow out of your woodshop unless you don't like breathing clean air. You should plan this and install this before you put your walls up and you might want to add a section of framing to accomodate hanging this. Look up Air Filtration systems on Rockler or any other major woodworking website and spec one out based on the cubic footage of your workshop. After this air filtration system you might need to add an outdoor whole similar to a dryer vent or such that will introduce a water failure point. I say do this early to insure all sealing is done completely correct and you can observe this. A dryer vent isn't anything new or crazy but a new hole in the wall is something you want to make sure is done right.