Before I hook it up, I wanted to confirm that I can hook up 12v to my UNO r3 on vIn and the adjacent ground. It won't affect the arduino negatively will it? The 5v output will still remain 5v correct?
As far as I can see Vin just bypasses the reverse polarity protection diode so that should be OK. Might be safer just get a suitable plug and plug into the “power in” jack and get the diode protection as well.
And yes, 5V is after the voltage regulator so it should still be 5V.