Most of those MOD paintjobs are done with a brush. As for building a garage booth, yes it's easy enough. My buddy and I painted our trucks in his barn with a booth just like you described and I need to finish my truck by painting the tub in my own garage soon. If you want shiny perfect clear coated paint then I would hire the actual spraying to a pro. If like me you want it all one color with a tough single stage paint job, a garage booth is perfectly feasible. Just get a good respirator.
The Goat, 2.8 Daihatsu Td, '73 coil conversion