It will automatically pick up your dustvotes, so anything that shows $0.02 or less will get upvoted on the 5th and 6th day.

As for the balance, just send in any amount over $0.10 sbd and it will give you your new balance. It will also give you 3 notifications when you are running low. It only takes out 1/2 of the upvote, so if you only had 2 taken out then you still have many many left.