There are some other threads here that you might want to read also, but here is my take.
My shop is above my garage so piping runs along the ceiling and punches through where I need it- but only in two places not along the walls. In my last shop I ran it across the ceiling.
I would not go with underslab ducting- you can't reconfigure, unless you put it deep you can't branch off with a gentle sweep wye or a wye and a 45, and T's are a NO, NO!, harder to clean, possible condensation problem, etc.
Pipe- Unless money is no object, use S&D rather than Sched 40. Sched 40 and S&D pipe are close in price, but Sched 40 fittings cost ALLOT more than S&D fittings. S&D is plenty strong enough- look at the crush strength printed on it. Use 6" rather than 4"- If you are piping to a whole shop, then you need a decent sized DC blower - 2 hp or larger with 12" minimum and preferrably 14" or 15" impeller (and possibly a cyclone) anyway.
Runs- keep them as straight as possible. It is often easier to run branches if you run the main diagonally across the room. Stay as large as possible as long as possible. If you must, only reduce at the machine. If you can, increase the DC port on the machine. Limit the use of flex.
I would possibly run electrical under the slab, but definately install underslab heating!