I'm no expert but I have encountered the things you're facing. I've had success repairing small chips by filling the chip with matching touch up paint so that the touchup paint is slightly higher than the surface of the car. Let it dry thoroughly then carefully work it down level using 1000 grit or finer sand paper and finish it with a fine compound such as Meguiar's Ultimate Compound followed by wax. For stains and other paint imperfections I've used Meguiar's Mirror Glaze 1 Medium-Cut Cleaner followed by Mequiar's Mirror Glaze 9 Swirl Remover. Being a novice I avoided using more aggressive compounds. I used a Simonize electric orbital buffer (didn't trust myself with a pro buffer as I was afraid of burning the paint) but for small areas I think it could be done by hand. Either way follow the product instructions, be careful and go slow or you could cut through the paint. Your success with stains will largely depend on how deep it has penetrated. For cracks I fill them with epoxy to slightly below the surface of the car and then refinish in the same way as a chip. Once again, I'm no expert but this is what I've done with reasonable success. I'm sure there are many others with more experience than I. Good luck and be patient, this will take time.