DIY Painting and repair - failing clearcoat

[scirocco]

The clearcoat is failing at some spots on my Alpine White X5. Never tried my hand at painting but why not. I plan to sand down the area to bare metal or close and do the three coat deal. So some questions to the expert painters here:

1. What grit sandpaper do I use to sand down to metal.
2. What is an acceptable primer to use? What brand and from where - in a rattle can?
3. Where to buy Alpine White touch up paint in a rattle can? What brand and from where?
4. What is an acceptable clearcoat to use? What brand and from where - in a rattle can?

Dont want anything too expensive. The truck has 250K miles on it. Drives sweet though.