Basic table manners: eating/behaving in such a way that it does NOT put others off their food (no burping, no rude comments either about the food or what anyone else has on their plates.
As for the specific examples:
1: Not unless it's a formal meal like Xmas, but even then I'm likely to say 'don't wait for me, it'll go cold'
2: For normal, everyday meals I always read a book at the table (newspaper too unwieldy) as reading and eating together is one of life's great pleasures. It's also the only chance I get to read, except on the loo. Wouldn't at Xmas or any other 'special' meal, though. At such times I expect to be entertained by the wit and wisdom of my companions.
3: Adults, unless afflicted with 'backs' and who therefore need to seek a comfier chair as soon as possible, are usually happy to stay at the table lingering over a chat and a glass of wine until the coffee course. I as the cook will be up and down constantly.
Children, however, may get down as soon as they have finished, and it is my experience that everyone is greatly relieved when they do.
I was once hit with the hitherto unknown to me 'don't leave the table without asking/everyone has finished' rule when staying with a strict aunt and four very cowed cousins. Meals in their house were stiff and uneasy affairs, in my own they were warm, happy and relaxed - which is how I wish it to be now I'm all growed up.