No teensy has that many pins, as most of the analog inputs overlap with the digital pins, Without the analog inputs (potentiometers), you would need to use 50 out of the 51 digital pins on the Teensy 3.5 and 3.6 (you need one pin for the input and one pin for the LED). The Teensy 3.5 has 27 analog inputs (the 3.6 has 25), so even without the digital pins, you would not be able to hook up all of the analog pins. And note, 18 of those pins are on solder pads underneath the Teensy that may or may not test your soldering skills.
So you need to use extra controllers that each talk to the master Teensy. You could go the i2c route. You could add 4 MCP23017's that each one supports 16 digital pins for input and output. And you can get 7 ADS1115's to give you analog reads. But at 11 chips on the i2c bus, that is getting to the point where you need to start worrying about engineering the i2c bus. Or with a bit of programming (since the normal libraries only support one i2c bus), you could use all 3 i2c buses on the Teensy 3.5 or 4 i2c buses on the Teensy 3.6 and put 4 chips per i2c bus.
Instead it may be better to break the problem and use some Teensy LC's to support some number of digital inputs and digital outputs, as well as analog inputs. For example you could have each LC support 10 analog inputs and 13 digital inputs or outputs. Then have the LCs talk to the master Teensy about buttons pressed, and inputs. It likely will be somewhat of a challenge to program multiple chips instead of one. On instead of LC's, you could just use 2 Teensy 3.5's, with each 3.5 supporting 15 analog inputs and 25 digital pins. You would need to communicate between the two Teensys, with one being master and the other being slave.
I would start small and redefine the program for a smaller number of inputs and outputs that can be handled with 1 digital i2c board and 1 analog i2c board. Learn how to talk to the board, etc. Then grow it slowly.