If you're not going to be doing painting with it, you won't need an oil separator, but some filters do that as well. For painting, you'll need the best filtration and water removal you can get. Guys have recommended a new or dedicated hose for painting. I have used an auxiliary in-line filter right at the paint gun for good measure.
If you're running permanent lines around the shop to your filter/regulator, be sure to include a drip leg with a drain valve below your branch takeoffs. Ideally the branch at the end should be coming from above, straight down to the drip leg/drain valve with the tap that you use, whether it has a filter/regulator on it or just a quick connect coming off horizontally above the drip leg. If you have intermediate branches, they should come off the top of the main, then with two elbows to drop down to your QC fitting. At the compressor, install a drip leg with drain before going up overhead. The extra pipe also acts as a water separator to some extent as it cools the air running thru it, and you have to get rid of that water that condenses out.
This is a Cadillac setup, but shows all of the best practices in shop air systems.
