In my experience, cutting acrylic needs a stiff router. I was cutting 20mm extruded acrylic in 5mm passes with a 6mm endmill and my 280kg table was vibrating a lot... :) If you are going to cut in 0.5mm passes there will be no problem, only time wasted.

The steel route is cheaper, faster and sturdier than aluminium if you are cutting, welding, drilling, tapping by yourself and of course epoxy levellling the rail beds.