Your credentials indicate you are handy in the area of engine repair and maintenance...and from the variety of engines you have worked with, quite adaptable!
Painting is a completely different skill, almost an art form if you may. Your willingness to learn is a good thing, and at least you know you can strip the body down to the shell if necessary is a noteworthy talent.
Yes, prep work is the most labor-intensive part of the process. A well-executed $1000/gallon paint job will look crappy on a haphazardly-prepped body, while a $50/gallon paint job can look marvelous on a well-prepped body!
The one real attribute needed to ensure good results is patience. There is a guy near my house that does nationally noteworthy show cars, and he can spend weeks on a door panel until he feels it's right!
The real question is, how do you feel about practicing on your MB? Regardless of the end result, your first effort IS a practice.
You don't need a paint booth...a good spray gun and a portable compressor will do the trick. If you have a garage, get some plastic drop cloths to line the area (floor to ceiling, paint particles get EVERYWHERE), and a really big fan! Don't forget the mask, paint fumes are pretty noxious, even after the job is done. Since your "paint booth" is not isolated from the envoronment, Pick a nice 70 or so-degree day in which to work, with little humidity. The best time of the year is when there are few bugs to contend with, so you won't arrive to see that a gnat has been crosstraining across your hood!
Try painting a smaller panel from a salvaged car first to get the hang of it. Because once you start painting your shell, you can't just stop...work from top to bottom, spraying each section in a linear motion from right to left (or left to right). Several light coats are better than a few huge coats, that could "orange peel" or drip. Give each coat enough time to cure before applying another coat.
Personally, I do better engine work than paint work (and I'm not that good at that either). I like superb results, so I just take it to a pro...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car