Unless you are happy starting on the back foot, I'd consider the lens before the copy stand; let's face it: you can buy an old Durst enlarger for pennies, and as long as it's not damaged and the planes are truly parallel, go for a longer lens such as the Nikkor Micro 2.8/105mm which gives you more working space between subject and lens. Actually, parallel considerations are not absolutely critical on the enlarger, because you can compose on your camera to ensure everything is squared up.
I have one of those excellent old lenses, it has a focus lock on it, doesn't slip pointing downwards, and once you are set up you are ready to go. A wonderful lens I'm happy to have bought.
Fitting your camera to what used to be a negative carrier is not rocket engineering. All you need additionally is a little light-box of some kind, which I'd assume as a film shooter, you probably already own.
Rob