I'm not talking pre-planned as in knowing everything, but interactions are generally talked about before they happen, at least in RPs I've been in (and I've been in quite a few). I definitely don't have a fixed plan - at the my only plan is that I think Tala and Cohen will get along, and that's it. It's all very vague.

Generally speaking, I think a courtesy "Do you mind if X comes and interacts with Y at this point, or are you in the middle of something?" in OOC would be polite at this point when there are a lot of characters in the process of trying to get to know each other.