0.5 micron filter is cheap, and put an oil coalescing filter before it as well, to increase the life of the wound filter element. SMC ones are cheap, and commonly available as well, and they offer the regulator filter as a package, with it having a gauge as well to show the output pressure. you will have a oil coalecing filter as first stage, which will also remove the condensed water in the incoming air, so the drain will need to be checked regularly, then the 0.5 micron filter in another stage and finally the filter regulator, providing nothing extra filtering wise with th5 micron filter they typically come with, but extra space to hold ant water that came past the first 2. 3 units in a line, probably cheapest is the versions with half inch NPT inlet and outlet, and 2 couplers to join the 3 filters in a line, a single bracket to hold them to the case, and inlet and outlet fittings to suit your shop air supply and the PNP air inlet, probably a quick connect for the shop air line, and a 8mm tubing connector for the PNP plastic tubing.