I advise the players to keep everything in terms of an action declaration as that is what I'm on the lookout for since that is when I have to adjudicate. I even discourage asking questions of the DM, if those questions can be answered by taking action in the game world. "How many doors are in this room?" is better stated as "I look to see how many doors there are in this room..." in my view. The stop-n-chat with the DM interferes with the flow of the game in my view, plus questions are often a form of out-of-game risk mitigation as the players fish for the best solution.That said, I'm pretty loose with player introductions in 5e because I strive to use my GM "no" as rarely as possible. Still, there's a limit in play and an understanding at our table because there are no mechanics available to resolve a conflict.
Anyway, I also follow the general concept that if it wasn't introduced in play then it doesn't exist and I have the option of adding it right now as long as it doesn't contradict some previously established fiction. So if a player says something like "I look around for someone I know among the guards..." and based on everything we know about the character, the setting, and what has come before points to that being reasonable, then I might say that's the case and, sure enough, ol' Frances just happens to be on duty. If it doesn't make much sense for that to be true, then nobody the character knows is on duty.