I cant really decide if I even want to put a plexi glass there. If I decide to put the plexi, should I put it behind the bezel (between the LCD and the bezel) or in front of the bezel? If I put it in front how do I attach it to the bezel...
The plexi is like the icing on the cake - you can do with out it but it will look a little unfinished.
It must go LCD -> bezel -> plexi
The plexi helps for all sorts of reasons -> firstly it looks good with clean lines, it proects your LCD from fingers touching it and any other objects that shouldn't, it is easily wipable for when you sneeze on it playing a game

So if you were to put bezel art on your machine it would go
LCD -> bezel ->artwork ->plexi
The artwork is sandwiched between the bezel and plexi (double sided tape can be use to hold it fast)
Now this is all providing your bezel is actually a LCD happ and is flat and not a CRT bezel that wraps around the curvy monitor.
Send in a picture if needed.