#3 is fine, #2 is generally good, but #1 needs some tweaking.

All drivetrain systems are originally designed to be run with compatible speed components. So it's assumed you'll be using a 10 speed RD with a 10 speed cluster, shifters and so forth.

You can't take a 10 speed RD and expect it to shift across a 7 speed cluster in indexed mode, the indexing will be off. You can do it in friction mode if the shifter has one, however.