That extruded aluminum T-slot material is expensive; there's no particular reason to use it unless you're trying to save weight. For structural parts that don't move, it's a waste of money in my opinion.
If you're talking about using a long piece of rubber belt as a rack, that's not a great idea. Just get regular steel racks, and use your motors to drive pinions spring-loaded against it.
A router designed for occasional use in a hand-held application won't work too well, or for very long, as a CNC spindle. I'd say budget for a real spindle and VFD, and keep your Hitachi in its un-destroyed state.
I'm not sure what that tilted fixture is supposed to do for you. Unless I had a special part that required machining at that angle, I'd wait on that until I really needed it.