This is exactly the way I painted the wheels on my Testarossa- but if you'd asked before, I probably could have saved you a bit of effort in scrounging for masking solution!
A very similar masking solution can be made by mixing plain white glue with just a touch of dishwashing detergent, and then adding a drop or two of food coloring. Apply, let dry, paint. Again, don't expect to cut it with a knife, but when it's wet, it's easy to manipulate- if you slop a bit where you don't want it, wipe it away with the tip of a toothpick. The coloring makes it easy to see when dry.
Your painted rims look spot on. Ferrari wheels are nearly always brushed aluminum (or magnesium alloy!)- so all chrome wheels tend to look goofy and toylike. But the chromed center makes for a lovely contrast. A light wash of black on the wheel nut makes it stand out a bit more (and not look like a one piece casting on the wheel center), and helps emphasise the gap between the chrome/brushed aluminum parts.
Lookin good!