Nine is Fine
Ten is Zen
Eleven is Heaven
Twelve is a Dozen
EDIT:
Hilarious! But to answer the original question, ten cogs would be enough for me (I'm on 9sp). I appreciate the idea/efficiency of keeping your entire stable on 10sp, but in your shoes I'd move to something more current. Life seems a little easier when you're up to speed, as it were, be it 11 or 12sp. You might find a way to appreciate more cogs, and you can get parts more easily.
Best of luck with your choices.
Last edited by BCDrums; 12-05-21 at 04:30 PM.