Hi Sam.
re point vs area
It varies for amenity=parking. Kind of depends on the layout complexity. If there is an existing concurrent rest_area as area I use a node. Note that these are all regional not urban objects.
re multiple points
yes a “formal” rest area that I fully create will have two objects. Usually a parking area plus a rest_area node. If a rest_area already exists I add parking. I include bin y/n in the parking object but toilets and picnic tables etc are separate nodes.
One of my root concerns was that the guideline (I think) has a clause about rest areas being a “different tag” if provided at a town park etc, so I concentrated on using parking objects.
Please have a read of my diary entry if you haven’t already.