I have a Toyo 45 AII and have used a 90 mm lens without any issues of the bed showing up in my negs.

With regards to the ground glass vs. a Tachihara, I have never seen a Tachihara, so I don't really know.

Re: the polaroid back, I found this on the B&H website: "Essentially a Polaroid 405 4x5 Pack Film Holder. Holds your choice of Polaroid 400 Series pack film. Fits any view camera's Graflok style back."

I don't know whether you will have issues using this back with the Toyo 45 A.

Max bellows extension is 360 mm.
Minimum bellows extension is ??? I'm not sure anymore. I know you would need a recessed lens board to use anything less than 90 mm on this camera.

It is a rigid camera.

Hope this helps.