So if I understand you correctly, in the Coin Control feature, you select 20K, then check the "custom change address", copy-paste your wallet address (the same one from which you are sending the coins) there and also to the "Pay to" field and type in the 20K into the "Amount" field, then click on "Send". Am I right? Why the "custom change address" divides the amount into half? Also, is 10K a good amount if I stake monthly? From my calculations, I would be better served by 5K blocks (so 10K in total) as it's roughly 16% a month and I can't exceed 1000 CAPs in one stake.

Thanks