Question #1.
So I am calculating deflection with 150 lbs of force centered across 6 ft with sides simply supported; I feel like those are pretty good numbers.
What would be an acceptable value. I am imagining 3+ hp router/spindle.
An 8020 extrusion 40-8016 (40 series 80mm*160mm) should do about .15mm in this scenario, and I am guessing that is a bit overkill and would weight about 48 lbs just for the extrusion.