Hi there,
So, you do understand they are they same with just more I/O pins brought out to the open access. Power and Silicon is the same. Those pins were always there.
they are the same…
There may be some additional abilities to shut off some IO power group sections but nothing out of the ordinary.
From the level of experience you have I would suggest to start with the plethora of threads on the topic for the Xiao Nrf52840 without the plus, or even Sense because those are easy to understand and all have code and compiler output. besides it’s the same Apple to Apple so not to worry there.
The peripherals are just that. (IMU, MIC, LED’s)
Typical battery Sleep currents are in the threads by @msfujino
get a good handle on the baseline required and any items you want to add sensor wise you already know the impact of.
then jump to the Digikey Battery life calculator , which you will see in those threads also to pick the best battery for your power requirements. Not rocket science but a process.
HTH
GL 
PJ 
Click that search Glass up there 
I have a demo on both Sleep and wakeup’s with double-taps , a button or a timer it’s all there.
look at ALL of the @msfujino threads if you want to truly know the finer points and nuance to doing it right , things like shutting down items in order and setting IO states before doing so , etc.
If you just want examples there’s plenty. 
it’s the same processes and results.
one example…
code , output and a video… 
Xiao nRF52840 Sense IMU Parked demo With SLEEP Interrupt button