We grew CC for the first time this year and it will replace Cherokee Purple from now on. I know it is a cross between Cherokee Purple and Carbon, but how stable is it? Do I need to buy seeds every year or can I save seeds from this year's crop?

It's an F1 hybrid, so if you save seeds you'll grow F2 hybrids from those (which should have a mix of the traits of both parents; each plant will be different). You can save the seeds, and I wouldn't discourage you from doing it, but it won't be Cherokee Carbon F1.

So, the leaves should be RL. The fruits could be black or purple. It's likely to be very sweet with variable taste. It should be a midseason indeterminate beefsteak/oblate slicer with large fruit.

I will have to think about this. Just so much room in the garden and so many tomatoes to choose from.

One thing you can do, if the seeds are expensive, is to grow a plant each of Cherokee Purple and Carbon, make the cross, and harvest your own F1 seeds.