The key card gate thing you can make it so the orange one is visible on game start but the green one isn’t. Put a invisible vending machine (make it invisible in appearances or all options) beneath it and make it deactivate when the green key card gate thing is unhidden. Next, make it so when the vending machine purchase is successful that it goes to the orange gate to make it invisible and make the green key card appear. Then make whatever door was originally blocking your way gone. You can use wires or channels.
Computers in OWO do a message, right? Then you can do a button under a computer and the button wired to a pop up.
Knockout manager on sentry. Make it increment a counter and in the property section do Knockouts. Last make it a number and player scoped. So when you knock out a sentry it counts it. Sorry, real last thing, in map options make it so it tracks the property Knockouts.
OR
if you can’t do that, make it so every time you knock out a sentry link it to a game overlay. After make the game overlay track an item and if you knock out a sentry you get an item.
Hopefully this helps!