I prefer the two bucket method. One just clear water, one soapy. Wash the car, rinse in one bucket, resoap in the other.
On the interior, including the windows, I use a microfiber cloth to clean. On the windows I use it dry and it pulls all the smudges and plasticisers off. On the plastics I use it damp. Usually no cleaners at all. I find it to be very effective.
The only treatments I ever put on the plastics is leather conditioner, and wipe off the excess. The non-silicone based treatment he mentioned is good too. That’s the same kind of stuff I use on the tires.
Meguires has some very nice microfiber products for drying the car.