Proceed to Step One. [:D]
Generally speaking, you’ll probably want to start with the cockpit, since it’ll be buried in the fuselage. Once complete and painted/detailed, glue it up to an inner sidewall (or whatever) and build the airframe. Radial engines can oftentimes be installed after the airframe is completed. However, this is not always the case, so just be mindful of when/how it should be installed. No need to put the small details (pitot tubes, antennae, etc.) on just yet, as they can easily get knocked off during the painting process. Now, some builders like to stick on the canopy after the airframe is painted. I like to add it beforehand, as I can more easily minimize any unsightly gaps between canopy frame and fuselage before I paint. And on that note, now is the time for puttying any small gaps. You can use Squadron putty, but I like Elmer’s Caarpenter’s Wood Filler, as it cleans up with water (while not dry), sandable, drillable, and won’t attack your lungs and sinuses. Just spatula in, smooth with a finger, wipe off excess with a damp cloth. Once the putty’s dry, sanded smooth, and primed (this is the best way to make sure your seams are, er, seamless!), mask your canopy and hit the paint booth. Once dry, give it a nice glossy clearcoat. You’re now prepping it for decals. You can use Testors, Tamiya, Krylon Clear Acrylic, Future floor acrylic, etc. Once dry, slap on the decals. After dry overnight, I like to hit it with another coat of gloss. This seals the decals. Now I can use a detail wash to accentuate the panels and surface details. I like tempera paint, thinned with water, but there are several useful recipes floating around on this forum. But tempera (or any water-based color) is the most forgiving. For tempera, just brush on, let dry, wipe off excess with a damp cloth. When all is dry, spray on a matte coat to tone down the glossy surface (unless you want it glossy, then use gloss). Now stick on the fiddly items, like antennae, landing gear, etc., and the cake is baked. Take a bow.
These are very general guidelines, just post any specific questions you have, you’ll likely get a hundred replies, there are many helpful people on the forum with lots of great ideas and hints.