If you have the 5e statblocks plugin installed and you make a custom monster in a note using it, it will have a save icon on the rendered statblock. Clicking this icon saves it so you can re-use it later using the monster field. See the ReadMe for more information.
The initiative tracker plugin can read these saved monsters and make them available when adding a new creature to a combat.
I have plans on adding a “creature view” of the currently active or selected creature that would show you more info about it, such as traits, attacks, spells etc (similar to Improved Initiative, if you’re familiar with that).
Reading from a spreadsheet is possible, but not ideal - it won’t be live, for instance, so any changes you make would need to be re-imported, and I’d have to make a specific format it would need to be in.