Ok, so a few things to unpack here
That first link never actually seemed to test the final product. It’s the Servisas guys, so could be great. But likely it will require software fine tuning, as all projects do. Also the buck converter he chose is only rated for 1A, so if you recreate it anyway, I hope you’re not planning on more than one board length strip of LEDs. You’ll want to check your current calcs.
The second link uses a custom pcb with an ESP32 (not quite Arduino, but close). Have you ever ordered a fully assembled custom pcb before? Additionally, if you dig deeper, most of the components on the BOM come up as question marks by that particular shop, so you’ll have to substitute or find similar parts. Again, hope you have some EE experience. The project hasnt been updated in some time, but you may be able to reuse the code.
Next - yes, you can use an Arduino to control individually addressable (“digital”) LED lighting. It’s a good, common solution. However, you probably don’t want to power your LED strips from the ubox spintend. If i remember correctly, its 12V port is rated at something like 3A. That could be enough, depends on how wild you want to go. If not you’ll need a dedicated buck converter rated for your battery’s voltage and higher current.
To get info from the uart, no matter the way you go about it, you’ll need to tap the RX pin of your VESC (like the first link).
With space inside an Esk8 enclosure at a premium, rather than buying an accelerometer breakout board and wiring it to the Arduino, just buy an Arduino with an IMU already on it. There should be a couple out there - one at least is the Nano 33 IoT.
With individually addressable LEDs, you can… individually… address… each pixel. So, yes, you can make half do fun glowy patterns and the other half react to uart inputs. It will take some work on the coding side of course. Any Arduino can easily control digital LED strips, if that’s all is doing.
If you’re not comfortable programming an Arduino you’re going to have a hard time making all of this happen. And definitely if you’ve never designed pcb schematics, don’t go ordering that custom pcb and expect it to work.
I’m happy to be wrong, but if you’re just starting out I would recommend start with a digital LED strip like Adafruit’s Neopixel or Dotstar, a run of the mill Arduino Nano / Micro, and get that glowing before going deeper.
Here’s is the message from spintend. 
