I'm selling stamp duplicates every now & then ...
However, when I sell stamps, I usually segregate, sort & classify them into categories (i.e. by countries, thematically ...etc) just for the sake of fun & spending time in scanning & describing them which definitely would come back with huge knowledge as well for you & the new owner (like two birds in one stone).
When I do such, I feel like I'm exiled from the present & going back in time when each stamp was issued (
something like I'm using my own imaginary Time Machine!)
After I'm done, I go back to present & bitter reality!
This is the BEAUTY of this hobby!

Anyway, I would suggest that you group them if you think they might come back with a profit or selling them in singles/issues if they worth something (y
ou can perform such a method if you are thinking of profitability).
But, if you seek learning & fun, do the way I do, & spend some happy hours in your own "Wonderland"!

Cheers