a paint store could probably answer this better than I, but I would say yes. it should get a light sand and then be washed with a product called tsp prior to whitewash.

If it's real wood paneling yes, if it's the shiny plastic veneer type from the 70's, no you would have to just paint it. My experience with old real wood paneling though is yellow almost always seeps through the white wash even after sanding.

I was also thinking of sanding and whitewashing some real wood paneling. Is there some kind of clear primer I can put on before whitewashing that would help prevent yellow from seeping through the whitewash? Would primer mess up the whitewash effect?

I think the reason wood yellows a lot is because of the polyurethane used on it.

Search your question on youtube as there are a lot of very good DIY videos by pros showing how to do all sorts of things.

Paint the paneling an off white and change the brass. Dark flooring will keep the room dark. I would go with light flooring.