Listen, I am a professional painter. I do it ALL day long every day. Not only do I work for a "company" I also do side work out of the garage where I have a complete setup, much as what I use at work. I know what I'm doing and have been doing it for at least 10 years. I am ASE certified and am not only a master collision tech but also a refinishing tech and I also am ICAR certified in paint refinish -- that's just a couple of my qualifications. Please, don't question my knowlege.
You should use 3-5 coats of base coat and 2-3 coats of clear. 2 coats will be fine if you use a single stage paint but not bc/cc. Technically you only need to wait about 10 mins between coats. So there is no need to clean the gun every single time you spray a coat. But of course, it's up to you, if you want to wait 2 hours and waste your time and clean the gun each time go for it but you don't have too.
As for the dust in the garage -- what Maverick said --
You should clean the garage real well prior to painting. IF you want to drench your walls w/ blankets you can but it's not going to be a huge deal if you don't. However, you should wet the floor down.
If you have any questions, send me a private message. I'll reply.