I love cargo biking!
...and videogaming, boardgaming, RPG'ing and helping users as an admin!
1. When entering the secret passage and placing your figure on it, the rule book doesn't mention if that is visible to the other player or not? i.e. do the guards know when you are in the passage or is the card behind the screen and they don't know unless they find the entrance and can search it?
You have to show this to the other player by placing your figure on it and open on the table. Only the maps are kept secret behind the screen. You need to say if they find a secret entrance but they need to search for it.
2. How do you keep track of which guard figures are patrols and which are sentries especially once a patrol moves off the red track?
As soon as there is more then 1 guard together you have a patrol and you can use patrol cards on them. So when you have 2 guards together they form a patrol. You can split up a patrol by playing a sentry card and pull away one of the guards from the patrol. The red track is a bonus movement for the guards when they are on it. Only patrols that are on the track move during this stage.
3. What happens when you run out of cards?
You have a problem and can't perform any of those actions anymore. They can still move and search but will be defensless. But this only happens to the intruder and ninja. The guard player(s) keeps shuffling his discard pile in his deck.
4. Are played intruder cards visible to the guards? Should the guard player know who played every intruder card as a matter of course? Or is it up to them to ask? Or are they not supposed to know who played it?
Yes, all cards are always playing in the open and the effect is said. So everyone knows who played what card.
5. An intruder has to search a room with a hidden sentry to 'reveal' the sentry correct? How else would the guard player know the intruder was in that room?
Yes that is the only way the hidden sentry becomes visible.