Aint it funny how we never seem to have enough. When we got say 1000 dollars all the things we want to buy are $1200. So we get a shop after having a single car garage and its pretty stressful now cause other interests start to rear their head and pretty soon what was a big space is now small.
We have a lottery over here in Canada well last week it was $50 million. I ask a friend of mines young daughter (21) what she would like to do if she had to win the 50 Million.
Well she said looking at a picture of an enormous yatch (not the kind with sails almost a liner) she would like one of those. So we asked her how you gonna keep it running. This thing had a full time crew of i dunno 20 or more people. Funny how soon it was not enough.
There is a bunch of tough choices there Darren. I have turned over one about 5 times when i saw you mention the insulation and then the partitioning. Part of me would insulate the whole thing heck and partition it. I like Larrys suggestion of partitioning the car area but undoubtably you will end up heating the workshop area. However with winter and a potential need to work on cars, I would want to be able to open the partition in such a way (simple door) to be able to share the heat when needed and not loose a ton.
I would also go the water etc route as a first step. Then concrete second primarily because it would put the whole area on the map for consideration since they would be on an even footing. Also that would make cleaning in that area way easier.
With a single pad for the whole area and 12 ft height i would think of using my partitioning such that i get a degree of mezzanine storage in above certain parts of the layout and you need to think of that when you do the partitioning wall if its gonna carry load and face the right direction for a load bearing platform. Something like that would make for wood storage out of the rain besides other "stuff" we all hord.
Another pro to insulating it is having storage that is non freezing in winter.
Remember how quickly these places get small so start off as if you were in Stus dungeon cause very quickly it will feel like it.
There is a saying that goes "a task expands to the time available"
so does a shop "expand to the space available"
I would still stick with all the space saving ideas we see guys with small shops do. Mainly because you still want to be able to move around and move projects you make around.
What a nice journey. Will follow along .....