Is this possible?

I'm working on a senior design project consisting of the Arduino Yun, 4 ID-20-LA RFID readers, a 16 channel multiplexer (CD74HC4067), and a LCD (http://arduino.cc/en/Main/GTFT).

I've attached my schematic (I'm waiting on the parts to come in) and I as I was drawing I noticed that pin 13 has a high number of connections needed. I just want to know will this be a problem?

You are using 13 as SCK to control multiple things in parallel? That should not be a problem. At the worst, you have to slow the SPI speed down some.

Why are you connecting RFID pin 2 (RST) to the Arduino Pin 13? The datasheet says you should connect it to RFID pin 11 (DC Supply Voltage).

I was basing the connection off this diagram from bildr

You should probably re-examine that bildr project to see if that connection was an accident or not. Does they code they provide do anything with Pin 13?