My two cents worth:

Go for the larger floor space. I think you will find that when you put a
table saw in the middle of any space, the saw, and the space you need to use
it, gets large. I built a 12x22 space years ago and was surprised at the
amount of space I didn't have once the saw went in.

I would insulate the roof and leave the rafters exposed (no ceiling). In a
workshop those exposed trusses or joists can provide a lot of good storage
for lumber, moulding and other long things. You can sheet parts of it for
overhead shelf storage too.

You might want to look into the way wood-frame, metal-sheeted buildings are
assembled. The lower framework is pretty much identical to conventional
framing. However they use wider truss spacing with longerons that are
usually on 2" spacing that adapt well to ceiling bats. For that matter you
get pretty good bang for your buck if you build the entire building for
metal sheeting and roof. The exterior finish lasts for years without
painting and you might find out you can build more floorspace for your
money. I helped my son put up a 20x26 garage last year. The two of us had
the entire lowere frame done in a day. The next day roof trusses and
longerons went up in 5-6 hours with about 2 hours of help from a couple of
his buds. He and a couple friends had the entire thing (less garage door)
closed in the following weekend. When you start hanging those large sheets
of metal it closes in quickly.

RonB