You will want to attach to drywall
No, this listing is for 6 boards total.
Yes, you will probably have to even though they are "finished". A light sanding, proper prep and sealing will give you a durable finish. If you plan to paint anyways, get the unfinished boards instead.
I would not use them anywhere. They are garbage. See my review on them.
Use nails on the small lips that will be hidden. Also use adhesive. Combination of both should have no issues.
Yes, you can paint this Timeless Shiplap.
No you do not see the grain in the wood.
I just took piece of it to the paint department and they color matched it. The problem was the sheen was a bit off, so if you want to use it to repair the many chipping the paint on the boards you better hope they are small chips or are in boards that can be used in an inconspicuous place.
Under the details on the item description page, it has the paint match recommendation.
I would Sheetrock first but probably not necessary