What you paint first depends upon your technique. If you do the smooth sections first, you have to mask them off when you do the nonskid, and the masking tape may lift the new paint when you pull it off. Oops. That approach also makes two separate areas of paint - no overarching, complete coverage of the whole deck in one film. If you do the nonskid first and then paint over that with smooth topcoats over the whole deck, you get the whole deck covered in one film and you don't have to mask the nonskid areas when you do it. It's less work.
EZ deck? If you don't want to do it all over again next season, you might want to be using a 2-part polyurethane paint. When our first 2-part poly coats on our deck started to wear out about 12 years after we painted it, we tried Interdeck (Interlux's version of EZ-deck), hoping it would be easier to apply, and cheaper. It did not hold up well. Since the prep work for both types of paint is similar, having to re-do the cheaper paint doesn't end up being cheaper because it has to be re-done. We spent this spring repainting our deck with Awlgrip, which we expect to last about 12 years. EZ deck may hold up better than Interdeck, but be aware. Forewarned is forearmed.
