Number of Player items required for MUT?

I was having issues adding cards to sets, with error message and getting kicked to the main menu. Unfortunately the error did not say why. I tried to auction a player and got a message saying I didn't have enough player items of that type to allow it. With this clue I bought a bunch of cheap players and finally able to complete my last motivator set to complete 99 RoH Vick.

Got me thinking how many player cards are required in your collection before you can sell or use cards in sets? I couldn't find any information beyond there is a minimum. Because I feel like I have way more cards now than when I started but depending on position I might or might not be able to add them to a set/

Atleast I figured out what was wrong with sets crashing to main menu