How to figure out max number of peripherals that can be run off a non-powered dock?

I want to know if it’s a good idea to go for a dock that allows power input. And more importantly, if one is not available or beyond one’s budget what is the best way to figure out when some threshold has been reached with regard to peripherals (analogous to running a bunch of electrical appliances off UPS).

There are also statements indicating that the PD 100W port can also be used for data-transfer but that does not make sense. I referred this post but it appears to have conflicting statements.

Basically I want to be able to expand my laptop’s available ports but not overload the chipset while doing so.