I'm with Kuki. You'd be changing tables in a hurry if you sat with us, because we'd be having way too much fun, and might inadvertently break a rule.
--We don't much care who sits to the left or the right, because we're not in the military, we've been equals for 37 years and we mean to keep it that way. At a round table, it all boils down to convenience. Sometimes there's a table mate one of us especially wants to chat with, so we'll seat ourselves accordingly.
--The easiest way to solve the "serviette" issue is to simply call it what 99.9% of the English-speaking world calls it, to wit: a "napkin." Using substitutes for a simple, straightforward word might be considered pretentious, which is itself an etiquette violation.
--While at times it might be fun to trot off to an alternative restaurant with your tablemates, I can think of a number of instances where it would not be a good idea. And I certainly don't agree that failing to join the group is a violation of any rules of good taste. For example, some specialty restaurants limit the number of times you can go during any one cruise. What if you've already planned a nice birthday dinner with your spouse? Surely etiquette would not dictate that you cancel it in order to go with the group. There's a difference between "rules" and "suggestions." They shouldn't be intermixed.
--Of course, fewer and fewer cruiselines retain the policy of directly tipping the waitstaff, and have gone over to the policy of adding the tips to your shipboard account. Some passengers don't like it, but that's the way it is. Of course, it still holds true that you shouldn't shortchange the crew by removing the tips from your bill as some particularly boorish people are wont to do.
Fact is, a lot of the stuff in the original post is basically correct, and most people adhere pretty closely to decent behavior. But it's also true that even though some lines still cling to the more formal dress policies, cruises are not the same as big deal dinners at the officers' club. Which isn't to say that they're places to be rude or inconsiderate, but the whole point is to have a good time, and if one or two of these rules are bent in that spirit, there's usually no harm done.