@Skulduggery usually when you select the payment method it will indicate the minimum and maximum withdrawal you can do with it. You can also check on the FAQ of the betting site on the withdrawals section or ask their customer support.
@Skulduggery it is possible to go on without draftkings, you could for example use an exchange like prophetx to place the 2nd back bet. https://www.ninjabet.com/prophetx