Metallic paint isn't that hard to do, but it does take a bit of patience. Here are some rules...

Don't cut in the entire room. Start with one wall and complete it before going to the next. Use only up and down roller motions, not side to side. You are right about keeping the paint well mixed. It's helpful to use a paint paddle in a drill to mix it all up from the bottom of the can to keep it uniform. If you have a helper, the whole process will go more easily if one person mixes and pours as the other rolls. Use tray liners. It's hard to clean up metallic paint from your tray. Get a couple of extra roller covers.

Allow your base coat a full day to dry before applying your top coat. It is actually a good idea to lightly back roll the entire wall in full top to bottom rolls after the whole wall is done, but do it without adding more paint. Lightly, without pressure, so you don't smudge the metal, overlapping to smooth it all out. All you are doing here is evening out the job, not second coating it.

Before committing yourself to an entire room, and risk of messing it up, try practicing on a spare piece of sheet-rock so you get the feel of it. You can even get one of those four inch rollers, which is nice to have around for hard to paint places like behind toilets and so forth anyway, and use that to practice. I actually used a spare closet wall to practice faux finish technique, then just primed it white the next time I had an open can in use. Seriously, one practice trial is a good idea.