My answers
1 - Yes, either LOC or fully established will do, it's usually a prompt for me to put you to TWR if the plan is working. But I'm sure you'll get other views.
2 - Don't work LL so can't speak for them.
3 - Do a search. It's been discussed here recently and it's not a black and white answer.
4 - Between two native or good English speakers I wouldn't worry too much - the tone of voice gives it away usually before you even get to the request. Where language/understanding may be an issue it's probably a good idea.