I've always had problems with some of the rules. Please help.
It has some quirks, for certain.
1. Can you see devices slaved to a host while outside the host?
I'd treat it the same way as commlinks - they are hidden under the icon it is slaved to, which is the host. Dangerous icons, such as guns, would be visible.
2. When it comes to finding icons over 100 meters away, can I simply use Matrix Perception "look" at a spot in the Matrix/real world over 100 meters away and see what icons are there? If not, do I just need some other way to know exactly what I'm looking for before I look?
Icons over 100m have a dice penalty, which implies to me that you can. If they are hidden and over 100m, you have to do a hidden perception first with the penalty, and then do a lock-on perception as a second test. If there is more than 1 hidden, you pick one at random unless you can narrow it down to specific in-game traits (e.g. commlink, cybernetic, camera, etc.)
3. The device icons I see within 100 meters, do they freely indicate what their real world counterpart is. Another way of asking is if I know there are 10 security cameras within 100 meters and I can physically see 5 of them, do I automatically know which icons correspond to which physical cameras, without doing a Trace?
Generally, yes, they are stylised so they fit the motif. A music file might be a musical note, a gramophone, sheet music, or a speaker. A camera could be a floating eyeball, a reel-to-reel, or a magnifying glass. If the person has a cyberdeck, they can run the wrapper app and that will re-stylise it to something non-conforming. I'm iffy about Trace beyond using on a persona.
4. How can you find "Protected" data according to chart SR5 page 241? Is this the same Protection offered by the Edit File action?
"Protected" data is usually in an Archive, inaccessible to the hacker. The way it's put is "You'll need someone who can get it out of the archive for you." Which means you just got hit with GM fiat.