Ahh yeah, I think you earn 1 extra giveaway slot for every 2 or 3 giveaways received by the winner, something like that. So you can eventually do more and more giveaways.

You could also send a support request to ask for an increase in your giveaway limit, if you wanted to give them all away at once. The limit is mostly just there to prevent spammers/scammers from making tons of fake giveaways to promote their youtube or whatever, as far as I understand.