I personally think you'd be better off with some authentic patina, either through continued handling or some artificially induced method. However, if you really want to paint it, I'd recommend going in a couple steps.
1) Start with a dark base coat. Some sort of aged bronze is a good start. Should be a bit darker than you want the final color.
2) Dry-brush the copper color you actually want over the base coat. This will mostly catch on the hard edges of the neck piece, but if you haven't sanded-smooth the base coat, some will collect along the sides as well. Purposely avoid the crevices, as the darker paint in those areas along with the shiny edges will emulate authentic wear and patina.
3) Clear coat. Satin is easiest to apply. Gloss works in low-humidity (it fogs up in high-humidity). I've had bad luck with matte clear not curing properly and remaining tacky.
Here's a Luke saber I machined from PVC and hand-painted using similar technique:
I wanted something *really* worn and dirty, so after drybrushing and clear-coating, I went into the crevices with dark brown and black paints to simulate years of dirt that were never quite cleaned properly, but you could leave that step out for a distressed-but-not-dirty look.