I think your paint scheme is very handsome. I like those colors together.
1. Pressure wash & scrub greasey parts with detergent.
Check the instructions on the paint you plan to use. I saw some that recommended using TSP (Tri-Sodium Phospate) for a cleaner, some that recommended using soap and water, and some that recommended using ammonia.
I ended up using soap and water.
2. Let dry for a week or so
I doubt you need to wait that long. Maybe just long enough to be sure nothing is going to drip down from under the rub-rails or some other place that could collect water. If you wait too long the bus will just get dirty all over again. It's amazing how much gunk is airborne, especially if you are near a street or anyplace dusty.
3. Roughen with 3M Scotch-Bright
I think that would work fine, but a coarse steel wool worked well for me, and it was much less expensive.
Oh, but I sanded with 100 grit sandpaper (just regular cheap sandpaper, not wet/dry or anything fancy) before I used the steel wool. My bus had been painted with some cheap paint that, besides being an ugly almost-school bus yellow, was chalking pretty badly. I sanded down to "fresh" paint, THEN washed the bus, THEN used the steel wool.
Sandpaper is cheap, very, very cheap, in relation to the cost of paint and the value of your time. Use it liberally. Don't try to get every last possible useful stroke out of it. Use it until it stops cutting quickly, then toss it in a bag to use later on other things. Also, a 1/3 sheet Black and Decker orbital sander (not random orbit, just plain orbit) is what I used to sand. IT MADE A WORLD OF DIFFERENCE. You can really get some work done with that.
For the odd shaped areas, I used a fine steel brush on the electric drill, not trying to remove paint that was stuck on well, just trying to get the surface paint off.
4. Paint. True-Value XO-Rust w/ Hy-Tech Ceramics applied with a foam roller and a brush where needed.
Again, read the paint instructions. I think other people have mentioned using the True-Value product, and I don't recall them having any problems. I almost primed mine (priming is not the same as painting, I know) with Rustoleum Primer for Rusty Metal because the guy at the hardware store said, "Oh, that'll work on a bus". After I bought the can, I read the instructions more carefully, and I discovered that Rustoleum does not recommend using that primer over paint or clean metal, but ONLY on rusted metal.
I ended up NOT priming mine. Once I sanded down a bit and saw that the paint underneath was adhering very well, I just painted right on top of that. I only spot primed two places that had some minor surface rust that I cleaned off.
PLAIN WHITE PAINT REFLECTS HEAT
Is the Hy-Tech Ceramics product you are using is a white roofing product, or a product that helps to cut down heat absorption? I wanted very much to use a white elastomeric roofing product (Cool-Seal, I think was the name) on my bus, but it was too expensive for me. I ended up using the same white enamel paint that I used on the rest of the bus. I'm pleased. I can't say how long it will hold up, but it certainly cuts the heat absorption greatly. The bus can sit all day in the sun with the windows and doors closed in 70+ degree weather and only be slightly warm inside. Before I painted it, it got uncomfortably warm under similar circumstances.
I reccomend using mineral spirits to wipe the bus down with as you paint. Wipe one 3' x 3' section to start with, and see how fast it dries. Then do another section about three times that large and let it dry while you paint the first. It dries in a few moments. You can just keep a some disposable shop towels and a can of mineral spirits beside you as you work along. The mineral spirits will make sure there is no residual grease on anything.
A 3' x 3' section at a time was about the size that was convenient for me to paint, especially on the roof where it's hazardous to be extending too much. From the center of the roof, I would paint a 3'x3' section along each edge, then move myself farther down the roof and paint the center section where I had been kneeling, and repeat the process. Work about halfway from one end to the center, then start at the other end and work back to the center, allowing yourself a path down one side of the roof to paint your way off the roof, so to speak.
You can buy disposable paper shop towels at Wal-Mart. They cost about a buck and a half a roll, but they are very durable, and I only used one roll painting my entire bus with two coats of paint. They look like paper towels, but they are blue and hold up 2000% better than paper towels.
The rollers I used tended to leave little nubby pieces of lint in the paint, particularly when they were brand new and when I was going back over the paint after it had gotten somewhat tacky. I used the cheapest rollers I could find, and a better brand of roller might not lose fibers as easily. One thing that helped was to brush over the rollers briskly with my hands a few times before using them to get the loose fibers out.
Also, you might try using a very short nap roller "for smooth surfaces". I used a 3/8" nap roller "for semi-smooth surfaces" because it's what I had, but it seemed to leave quite a few air bubbles in the paint. I solved that problem (mostly) by "double rolling".
I don't know if this is a good or real technique or not. I would paint a section, then move on to another section and paint it. Then I would go back over the first section with the ***depleted*** roller that I had just finished the second section with -- the goal is not adding more paint, but smoothing the paint that was just laid down. The paint on the first section was a little tacky by that time. One thing this did was to pop any little bubbles in the paint. Another thing it seemed to do was to smooth the paint out even more, and allow me to catch any runny areas before they actually ran. The disadvantage to this was that if I waited too long to re-roll, the paint was really tacky and seemed sometimes, but not always, to pull some fibers from the roller. It's something you just have to experiment with a bit before you get the feel for it. I think it made a big difference in the finish on the bus, though.
Get some FINE steel wool and go over the first coat lightly AND wipe it down with mineral spirits again before you put on an additional coat.
That's about all I can think of. Hope it is helpful.