Hello,
"Hold 10 non-memorised cards in your hand" means that mnemosyne will not show you more than 10 cards witch are not learned. For example, if you have 100 unlearned cards, mnemosyne will not show you 100 cards in an "randomized" order, but will pick 10 of them for you to learn. If you grade 2 and higher another card of those 90 remaining will be picked and be among those 10.
Hope that was clear (?).
>Does de-activating a card also delay the review of that card?
When De-activating a card, the card will no longer be displayed, unless you reactivate it again. But if the card has another tag that is activated it will be displayed.