It got tricky quite a while ago 
The initial project was easy enough, it has well defined inputs and outputs and is a suitable size and complexity for an Arduino. Even the addition of the neopixels isn't too bad (most of the complexity there is in the hardware and Adafruit provided library other than the power issues) and is still suited to an Arduino. Once you get in to tft screens things start to get complex in terms of input data and drive and you start maybe getting beyond the capabilities of a 328 (as in the Uno). By and large power is the easy part of this, a wall wart will usually supply suitable power (it gets more tricky with high current things like neopixels, but screens aren't a particular power problem). Your current issue is figuring out where the data that is going to appear on the screen comes from, if from the Mac, how does it get to the Arduino? Is it in a format that can be displayed or does the Arduino need to modify it (memory is then likely a problem)? Can it get there fast enough to meet the performance requirements of the various screens? Is there something on the Mac that will generate the data (I'd expect the Mac side to be the most difficult to make changes in but may be wrong)? The audio level data that appeared to being displayed on the screen needs to come from somewhere as it isn't in the Arduino at the moment. Most of the screens take either 5V or 3.3V for power just like the Arduino. They can probably (although the Arduino 3.3V supply is limited to about 30 ma of current) be powered from the 5V or 3.3V supplies on the Arduino. At worst a coax power jack and a 5V and/or 3.3V wall wart will get you your power. The hard part is going to be getting the data I expect.
Peter