*Cracks knuckles*, OK, Supe's "new guy polishing recommendation post", retyped for the nth time...
DA's, even the Flex, are very gentle machines. They don't have the correcting power of a rotary, and that's a good thing; they are much safer to use than a rotary, with a larger margin of error. IMO, you got the best DA machine out there. The Flex is known for having better correcting ability than the other machines.
Now let's talk pads. For lower powered DA's (Meguairs, Griots, PC 7424, UDM, etc), it is often recommended that you stay with 4" pads to get better correcting power. You can press harder without bogging down the motor on a 4" pad than you can a bigger one. The Flex does have more power, though. You could probably get by with bigger pads, but still, if you want maximum correcting power, stay with the 4" pads. You probably won't need anything more than the following pads: 4" LC orange, 4" LC White, and 4" LC Black. Get at least two of each.
Now let's talk about polishes. Once again, DA's don't have alot of correcting ability. Therefore, you want to get polishes that have maximum bite in their respective categories. In other words, you will want to get a medium correction polish that is the most powerful of the medium correcting poliishes. Right now, that is Menzerna Super Intensive Polish, or 1Z Intensive Paste. For medium polishes, you just can't get any with better "bite" than those two. Pick one of them, and it's going to be your mainstay for "correction"; getting out defects and swirls. Apply it with the orange LC 4" pad at maximum speed. Don't be surprised if you have to do multiple applications to get the defects/swirls out; again, you're using a DA machine, and it takes alot of work to correct paint with it. Especially if you're "blessed" with a hard clear coat on your vehicle. I wouldn't get anything stronger than the above polishes. Going up to a really high powered compound like Menzerna Power Gloss, Meguairs M105, etc., really isn't a good idea for someone just starting out. You're better off doing multiple applications of a medium polish than reaching for a big gun.
Now let's talk finishing polish. After you have corrected the paint (remvoving the defects and swirls), you'll need a finishing polish that again has the most umph in it's class. Right now, that is Menzerna PO106FF (also known as Nano Polish), 3M Ultrafina, and 1Z Hochglanz. For someone just starting out, I'd recommend the 1Z Hochglanz, but you can't go wrong with any of them. Apply it with the 4" LC white pad to remove any remaining compounding marks, then apply it with the 4" black LC pad to really put a shine on the finish.
After your final polishing step, go over the vehicle with a 50/50 mix of isopropyl alcohol/water and an MF towel to remove any left over polishing residue/dust.
Apply an LSP of your choice.
