Use the "passwords" feature to check if one of yours is compromised. If it shows up, never ever reuse those credentials. They'll be baked into thousands of botnets etc. and be forevermore part of automated break-in attempts until one randomly succeeds.
Also, length is most of what matters. A full length sentence in lowercase with easy to type finger/key flow for pw manager master, and don't know a single other password. Can someone correct me if I'm wrong?
I've found that there are a handful of passwords that you need to remember, the rest can go in the password manager. This includes the password for the password manager, of course, but also passwords for your computer/phone (since you need to log in before you can access the password manager), and your email (to be able to recover your password for the password manager).
You are also correct that length is mostly what matters, but also throwing in a random capitalization, a number or two, and some special character will greatly increase the required search space. Also using uncommon words, or words in other languages than english can also greatly increase the resistance to dictionary attacks.