Battles can be targeted during the Attack phase and the defending player can assign Defenders to it
Currency Converter Currency Converter does its best work alongside commanders like Raffine, Scheming Seer and Flubs, the Fool that encourage you to discard a bunch of cards
And then you have Barnabas Tharmr if you throw Kraum into the mix, I guess
However, if those permanents entered in the opposite order, you would have no maximum hand size
I'm not sure about the status of your playgroup, but I also would suggest sweepers like Cataclysm, Tragic Arrogance, Mutilate, Cyclonic Rift, basically any sweeper that says "Sacrifice", "Bounce" or "-X/-X" to account for cards like Avacyn, Angel of Hope