The above advice from mrsmithz is pretty much straight on. I usually wait until I am done with decaling to do the panel lines or else the decals sit over the 'dirty' lines. I like for the panel line wash to go over the decal, then it looks more 'to scale'.
The Tamiya rattle-cans are superb and the spray settles down beautifully. It works perfectly in lieu of an airbrush. I airbrushed three good coats of Future on my Ozma before beginning to decal. If you use a paint brush, be sure to not stir the future and create airbubbles. You can easily get distracted trying to brush them out. The Future also lays down very good and levels very well. If you use the Tamiya gloss coat you will get the same results. Just remember to mist coat it and keep the can moving, or else you will get puddles of clear coat, and that sucks.
Here's my progress so far. I'm almost done with decaling- a few left around the middle of the top fuselage and the intake area. I painted the area behind the head and the small intakes on the legs that appear just to the rear of the skull marking. The decals are thick and you can see the screen printing but they settle down beautifully with additional coats of Micro Sol. I painted the cockpit with a little grey and some Tamiya Gunmetal. Love the color. The only other area I painted were the thruster/vector nozzles on the end of each leg. I started with Gunmetal and then thinned some Chrome Silver and hit the highlights. Once that dried, I loaded some thinned Citadel Chaos Black and misted the edges of the thrusters. The Citadel black dries very, very flat and looked like soot. The effect was to try to replicate heated metal. Once all that had cured I used some of the Tamiya weathering powder (heated blue) and hit some of the high spots. I'm pretty pleased with the effect and wish the camera did it more justice. In the end, I am probably going to 'glue' it in the fighter mode. The decision will hinge on how well the decals stay after 3 coats of Dullcote.