Re. table etiquette, most should definitely be challenged as they are hangovers of the English class system and horribly outdated.
Things like using the back of the fork only, sipping from the side of a soup spoon, tilting your soup bowl away from you, were all designed to slow down on the eating process, because only poor working people tucked into their food with gusto. Any sign that you were hungry, like bringing your food towards you or taking large mouthfuls, were considered common and just not done by the gentry.
But much of the food we eat today is from cultures where the standard knife, fork and spoon isn't used, and many dishes can't really be successfully eaten the "refined" way. I recall sitting opposite my SIL when we were having spaghetti bolognese, and it was almost painful watching her with her knife and fork, trying to cut the lengths of pasta to a size that she could balance daintily on the back of her fork, only for it all to fall off whenever she tried to get some of the sauce on too. Over and over.
Agree that chewing with an open mouth is awful, and sticking out your elbows is just rude. Similarly, bending your head almost down to you plate to get food in always looks a bit like a pig approaching the trough, but I can understand why if it's something that's very drippy. Talking with you mouth full is awful if there is so much that people can see your food, but can be OK if it's just a small amount, and you're among friends and it's a casual event. Likewise elbows on the table.
In any formal setting I'd follow the standard rules, but I eat my food according the way the cuisine intends, so no knife for pasta, will always give chopsticks a go before giving up and grabbing a fork, and I will shovel in my peas, because there is no reason other then snobbery not to.
Saying that, if I've made a delicious sauce, I'll lick my plate afterwards! But only when I'm home alone. 😁