You don't have to use another microcontroller if you don't want to. The Pi can theoretically drive all of this, but it would involve some pesky Linux configuration to drive the two smaller TFT displays in addition to the main one. The PiTFT only uses a handful of IO pins (mostly for SPI data), so you'd have some IO left over for LED's and buttons and whatnot. Worst case, get a GPIO IO expander and connect it to the I2C pins on the Pi. Something like the SX1509 board from Sparkfun. That should give you more than enough IO to use. If you want the Pi to talk to the Feather microcontroller, the easiest way is probably to connect them over the serial port (rx and tx pins, but make sure they're both operating at the same logic voltage. The Pi uses 3.3v as its logic voltage, so make sure your Feather also runs at 3.3v for logic voltage.) The PiTFT leaves those serial pins unused, so you can still tap into them and use them. You should be able to use a USB cable, depending on the power source. The Pi and Feather boards all run off 5v, and the smaller TFT screens have a built-in regulator to drop the voltage down to 3.3v. Just make sure you have enough amps to drive all of this though. Most computer USB ports only provide about 0.5amps of current, which isn't going to be enough to drive all of this. If you're going to drive the two small TFT screens individually (not having the image mirrored from one display to the other), I suspect you're going to need a Feather for each screen. Unless you're feeling ambitious and want to try to do it all with the Pi, which is probably possible but not trivial. Yeah, you can use that if you don't feel like having a custom circuit board made. If it were me, I'd probably connect all of my LED's, buttons, and other sensors to the Pi along with the main TFT. And I would use two Feather boards to drive each smaller display. The Pi would then just commands over serial to the two Feather boards to tell them what images to display. Just my opinion, though. There are lot of different ways to do this.