Is there a way to be able to set a short memorable password for my chromebook user, rather than have to type my 50 character full alphanumeric password generated with by my password manager ?
Enable two factor authentication for your Google account. For ultimate security use a Yubikey. Now you don't need the giant password. Combine this with enabling PIN login as suggested by @DanHolli.
Also, Chromebooks use very little power with the lid closed. I leave mine on and therefore rarely have to log in.
Have you tried Smart Lock? You just unlock your Chromebook when your unlocked Android device is near and has Bluetooth enabled.