MOSFET dimmer IR controlled
The first error I see with the sketch is right under this line of code Serial.println("Triggered D");. You are incrementing the variable brightness when you probably meant to decrement it.

The second error is with your call to analogWrite(). This function accepts an integer between 0 and 255. You do not constrain the value to that range, and can see what I mean by adding this line of code Serial.println(brightness); right above this one irrecv.resume(); in your sketch. Going from 0 to -5 turns the LED from off to maximum brightness. Is this what you want it to do?

The errors with your MOSFET circuit is a "General Electronics" question, and should be asked on electronics.stackexchange.com. As I mentioned in one of my comments to your question, there is a recommended format for drawing schematics.

My other comment was regarding this Q+A at EE. You won't find a consensus on exactly how to use a MOSFET there either, but the image in this answer may be helpful to you.