Hi Ken;
I think a slab would work for you but I am not an engineer. My advice is to hire a engineer. I think adding 3x3x3 footings under a slab would add enough cost that an engineer's fees would be well worth it. It sounds like you really need an engineers stamp anyway. We are fortunate to have a number of engineers who are very knowledgeable about traditional timber framing in the Guild and they are probably your best bet for foundation and frame design.
Take care;
Jim
