Cool thanks, I’ll try using a 3.3v supply then 
. I found a “battery shield” that takes 2x 18650 cells and gives provides USB power, 5v pins, and also some 3.3v pins that seems like it’ll be good for what I need (and a hell of a lot cheaper and easier than putting together my own BMS). My hope is that the built in voltage converters it has for 3.3v and 5v should prevent power draw from occasionally running a 5v servo from interfering with the Xiao and sensors that’ll be connected to the 3.3v.
BTW the pins being numbered 0-13 seemed perfectly normal for me, I’m a programmer by trade so I’m always using 0 to refer to the first item of a list