I run a Nuovo Record crank with a 9s rear cassette, and I think an Ultegra 6500 or 6600 rear derailleur.

One can do quite a bit of mixing and matching, especially with friction shifters. The biggest limitation is whether the shifter has enough cable pull to push the derailleur across the entire range of the cassette.

Shifting? Heck, I don't know. I like to light pedal briefly while shifting. I don't think the front shifting is any worse than it was 30 years ago, and the rear shifting is actually quite a bit easier than it was with the vintage freewheels.