Thankyou for everyone's replies. They have been very helpful. I have come to the following conclusions, which I will be implementing in my campaign unless someone can convince I am in error?
Core Concepts
• You cannot Hide from a creature that can see you clearly (requires at least 3/4 cover).
That's ok though I would personally also say that forms of concealment should qualify.
• Stealth is an Action. When you try to hide, make a Dexterity (Stealth) check.
Correct, a rogue can use cunning action to do it as a bonus action.
• Passive Perception is the DC your Stealth roll must succeed against.
correct
• Search is an Action that allows a creature to make an active Perception skill check.
correct.
• Only the First attack roll on a creatures turn has Advantage if they are able to successfully hide.
this is incorrect. The first attack you make when you're hidden has advantage. If you can somehow hide, attack and then hide + attack again on the same turn then both of those attacks would have advantage because you managed to hide before both.
• If the location a creature is attempting to hide in is obvious, the creature has Advantage on their passive Perception check (DC +5). Example: creature hides behind a tree and doesn’t reappear, ducked around a corner, vanished from sight but didn’t hear you move away, etc. This is also subject to DM fiat. Example: If a creature repeatedly ducks around the same corner and pops out to sneak attack, it can be assumed the target is expecting the tactic and the creature automatically sees the attacker dart out as they are expecting your re-emergence.
This isn't something that I do as a DM but it does fall within your prerogative if you really feel the need to impose this kind of penalty to the rogue.
• Disadvantage on Perception checks if target is 50 feet or further away.
There's also disadvantage when trying to perceive things you can't see properly. Such as trying to make out someone in darkness. See the point below
• Dim Light (shadows): Imposes disadvantage on Perception checks.
correct, dim light and darker.
• Darkvision: Can see in darkness as if the darkness were dim light. You see in shades of grey.
As someone else noted, darkvision also let's you treat dim light as normal light which can counter the benefit of the Skulker feat for example.