Entrance is €8 per person. Included is a glas of port to taste.

I would say an hour. Maybe 1,5h if you take it really slow.

Yes, multiple elevators to every level from the street.

Some Quintas are open for tours and tastings and some are not. Most require a reservation and if you have language requirements, English for example, those tours are only offered at certain times of the day. I hired a local guide who arranged the tours for me and drove me to them and then back to my hotel in the area. We were able to visit up to 3 Quintas a day and have lunch as well. You can try to research and make the reservations yourself, but I found hiring a guide was well worth the money.