Originally posted by Ray Bersch:
You know, I never thought to mention the floor structure - probably because I just assumed it would be concrete - so you know what happens when you assume something!
I think you will be happier in the long run if you beef up the floor a bit. At the minimum I would add another layer of 3/4" plywood and glue (construction glue)as well as nail the second layer. Also, put solid bracing (use the 2x8 material) between the joists. The floor you contemplate would be minimum for residential purposes, adequate but not totally satisfactory, for your use, even with the center support you mentioned. You will find the floor will bounce, maybe sag under heavy equipment placed away from the perimeter, and promote annoying vibration.
The cost for the extra layer is minimal compared to its value - my opinion, of course.