On measuring power and system load to correlate them (something the article mentions) - I would hook the Pi up to something that can measure outlet power consum

On measuring power and system load to correlate them (something the article mentions) - I would hook the Pi up to something that can measure outlet power consumption and report via USB, and then feed that back into the Pi’s own USB port. Metrics can then be collected and stored, and easily analyzed with eg. grafana. I have such a setup with an old watts up meter, telegraf collecting raw data off a custom script that talks to the watts up via usb, Prometheus for data storage and grafana for analysis. If telegraf/Prometheus are overkill for the Pi, a cron that gets the power measurement and stores in an SQLite database would do the trick. Or one can go even more classical and use rrdtool to store and plot data, which can then be exposed as static files via the existing nginx setup.