Elba If you have anything less than 5/8" good luck, 1/2 will be wavy no matter after a few months. The entire process of sheetrock finishing for gloss paint is very much like painting a car, patience, a lot of work, perfectionism, skill. I do not see where all the effort could be worth it. I spray my entire house in eggshell, much like gloss as sprayed it is like glass smooth; for your home, it is worth the effort but for a garage, I would not go for gloss. Go with rolled eggshell, prepping for rolled eggshell is still a lot of work, but hides better then gloss. In the end your the only one who will appreciate it, and you will see any imperfections.
Is this possible and if it is How ? Not trying to be mean but If you have to ask, you do not have the experience/skill. An explanation would involve multiple type written pages.