@Twonewcats I've got no personal experience on the show or on any reality TV, but I did work in film and TV for a while so I can take an educated guess at this.
The crew will be AT LEAST twice the number of Traitors, probably three times as many. Every room has lights and cameras in it. Some are likely static - the hallway one seems quite fixed up on the ceiling? There are PAs scurrying around fetching water and food and checking in with everyone.
There's most likely 2 identical 'diary room' sets, as a PP said - one at the castle and one at the hotel. I'm sure that they are all called there on a rota during their 'down time' to record how they're feeling - that's the only way it would work to avoid suspicion of a certain 3 people getting called in all the time!!
All the shots of them in the bedrooms: Andrew pumping iron, Diane doing squats, Charlotte bathing - were all most likely shot on the first day or so, probably before the traitors were picked - then they just cut them in for atmosphere when needed...
It was so weird to me that the Traitors congregated at the fire pit yesterday to plot but my hunch is that is where a camera crew had been set up - a crew member told Miles to get Paul and take him there, then when they were someone else on the crew told Harry to join them - it's got to be directed to that extent I reckon.