The sad thing for a scope of that size is that most parts are going to have to be fabricated rather than bought.
Scope of that size often become truss designs as this ends up making a rigid yet light scope but you do have problems with light polution of the optical path. Better to do a solid tube instead.
For the tube, a machine shop or sheetmetal shop will be able to roll some aluminum for the tube and weld it together. In addition, the pirmary mirror support can also be made in the machine shop.
The Naysmith focus is more for scopes that don't have a hole in the primary as a flat mirror directs the light to the side before it gets back to the primary after the secondary and out the side of the scope. If you already have a hole in the primary, it is better to let the light go through to the back as there will be less light loss that way.
An Az/Alt mount is one like a turret on a Navy ship where the scope goes around on the vertical axis and goes up and down on that mount. The Equatoral mount points one of the two axis parallel to the polar axis of the earth so that it is the only one needed to move to keep a star in the EP as time goes on.
In either case, you are pretty much in the home made region for making a mount. I'd recommend the horseshoe mount like the Hale scope has as this is a very rigid mounting system. The scope may be lifted from the axis a bit with forks if so desired but you don't want to go too far or the problems with forks starts showing up.
A decent alternative is the German Equatorial mount but that is the scope hanging off of one side of the of the mount with a counterweight hanging off the other side. The problem with this mount is that there are places where the viewing needs to be stopped and the scope flipped to the other side of the mount.
Good luck with your efforts as that scope will be an excellent scope for doing a fair bit of science with.
I'd also plan on getting a large CCD camera for it to assist in getting the best out of the scope.