Where do I get rough number/intuitions about how much power I can use where?

It's complicated, because you can draw as much current as you want until you blow something up, or until the I-R drop (as in, V = I*R) gets so large that the voltage is too low for some circuit to function. The GPIO pads will sink up to 4mA. But you're asking on the #caravan channel, so I'm guessing you're asking about just how much you can dump into an arbitrary circuit through a bare pad. For that, go see https://docs.google.com/spreadsheets/d/1oL6ldkQdLu-4FEQE0lX6BcgbqzYfNnd1XA8vERe0vpE on tab "Layer resistances and capacitances", section at the bottom "Electromigration rules (estimated)". That's how much current you can dump through a given metal wire on the chip without breaking electromigration rules. The bare pads attach to layer metal3 on a tab which is 25um wide, and the rule for metal3 is 1.5mA/um, so you can run about 38mA through the pad (assuming that doesn't burn out the circuit inside, all parts of which have to satisfy the electromigration rules). Three of the pads on Caravan are designed for high-current applications; they have 140um of metal3 and can take up to 200uA. Electromigration rules are specified for long-term use, meaning that for a test chip you can get by with higher current numbers, but generally it's a good idea to design for the electromigration rules, and don't exceed those numbers during testing.

Fantastic, thank you.

Yes, sorry.

How should I have found / known about that link?

Good question. We need a repository of important links. Beyond the stuff on readthedocs.

Any other good links or info about this?