Hello, i'm a complete beginner to Arduino. My aim is to make my own button box but really want to use the 12v LED levers and switches. Now from looking around and asking on Discord the best way seems to be using MOSFET resistors, in particular the IRLZ44N.
Now that brings the other question firstly of how i could calculate how many amps the power supply has to be and which ohm resistors to put.
Secondly as i understand the Micro has internal pullup resistors for if you choose to power the board with 12v through the RAW pin, could that output 12v through other pins? If not for what use is it?
Lastly i've also seen button boxes with LED levers that use 1 single usb cable, which makes me wonder how they supplied 12v? As i cannot find LED levers or switches that are 5v or less. I assume 2 cables are mandatory, 1 to connect to the Micro and 1 for the power supply.
So could it be those are made with something else then Arduino or am i missing something obvious?
Like what happens if you connect a 12v led to a 5v power pin? Does that make the 12v LED just be dimmed but do function or wouldn't that work at all?
Finally (i promise) is there some component like the DC connector but as a micro usb port that could function as a power supply connector. I guess there must be but can't find it for the life of me.
OK, first task is to learn how to ask questions. Read the instructions for posting referenced at the start of each forum listing.
We probably do not know what "12v LED levers and switches" are! You need to give Web links for each component you have in mind.
That is likely to be a very bad idea! It actually requires a regulated 5 V supply. You may think (reading some "tutorials") that it has such a regulator on board already, but then you are almost certain to want to connect other things requiring 5 V, and there it falls down.
It is all 5 V logic.
They probably did not. But then you have seen them but we have no idea! Only when we can see meaningful details can we advise.
Generally does, as long as there is only one LED and a series resistor.
A USB port can generally supply up to about 500 mA at 5 V. Some USB versions can supply more, but that becomes very tricky.
It is possible to transform that into 12v though. If the parts connected really need 12v that can be done, but normally a part like that also comes in a 5v version.
because ? USB is 5v. A switch is a switch. and a LED that lights up with 12v needs a current limiting resistor somewhere. Anyway show us want you want to use.
It is all 5v Logic, pullups are up to 5v. If you connect a switch to the pin and GND, and enable the PULLUP, the pin reads HIGH when the switch is open, and LOW when the switch is closed. If the PULLUP is not enabled and the switch is open, the logic level of the pin is undetermined, whatever so to say.
Read the 
Only when we can see meaningful details can we advise.