Shop within a shop construction - beginner help

First post here! Thanks in advance for taking a minute to help me out!

I am in escrow on our dream home – the house is what my wife wants and the 40×40 uninsulated steel shop is what I am drooling over.

We live in the desert where it regularly gets above 115F, and sometimes over 120F. My plan is to convert about half of the shop into an insulated woodshop (20×40 or maybe 17×40) that I can cool with an efficient mini split a/c. Additionally, I am thinking that I will use the space above the shop ceiling for storage and eventually put a smaller 10×10 clean room above the woodshop to do 3D printing and computer design (I mention this only so that weight bearing is a consideration).

So, for phase 1, the base 20×40’ shop, I am looking for advice on framing and construction. If I am doing 10’ tall walls, will it be worth it to use 2×6” framing or even 2×8” framing rather than 2×4s? The price difference from 2×4 to 2×6 is about 70% more. It is only about 6% more to go to 2×8 from 2×6s. The factors I want to consider are sturdiness, insulation capacity, and cost.

Finally, I was thinking that I would use OSB to do the interior walls and just drywall outside. Anything wrong with that idea?