You'll be able to fit 10 of your cards without adapters, but you'll need 10 adapters for the other 10 cards. Starting from the top of the board, you'll put in 2 cards. That will fill the first 4 slots.
The two PCIE slots at the bottom will be open still, but you want to use both of them. If you put in another card in the second to last slot, you'll be covering the last slot, as your card is going to be 2 slots wide. So if you want to use both those last slots, you'll need 2 adapters, one for each. 2 adapters per board is a total of 10 adapters.
And you should be able to run these adapters.https://cablesaurus.com/index.php?main_page=product_info&cPath=1&products_id=10&zenid=bc08b0c77731d37c4ed5e9673608cee0