Nice first bodies, they look great for early efforts. The .5 needle at 50-65psi is your main culprit for the fine line issue, that's a lot of air and paint moving at once. Try dropping to a .3 needle and around 25-30psi, you'll get way more control. For cutting masks, I do short overlapping sections on tight curves instead of trying to never lift the blade, and backlighting the body helps a ton for seeing where you've already cut. The sharpie method with cutting both sides is solid, maybe try a lighter color sharpie so the cut line stands out more. You're on the right track for sure.