Build a simple square top at about 42-48” high. Minimum 3’ to allow enough room for bipod and rear bag. Build it out of cinder blocks and pour concrete for the top if you want it 1st class.
The Decibullz percussion molded plugs are pretty good. I ran them all weekend in the 2 day Hornady match and never had problems hearing commands or noticing blast.
The turning arbor will be .221 or .002 under. This is what I use in my setup after FL sizing to uniformly expand case necks. I have the Tin finish mandrels and have great results without having to lube. They also have a black nitride finish that is supposed to be even better. I have one on order...