How should I store my rMBP for a month? I am leaving for a vacation and leaving my rMBP. How should I store it except from shutting it down? How much charge should I leave in order not to lose too much capacity?
You are overthinking this as there is nothing special about the lithium battery that requires special storage considerations.  Just store it like you normally would; I put mine on a bookshelf to hide it from the inevitable human curiosity of the dog walker/plant waterer when I go on extended trips.

Your lithium ion battery is going to lose capacity whether you use it or not because the biggest factor in the longevity of a battery is age not how much it's charged.  Now, the amount that it loses over the month is going to be negligible; you won't even notice.

I posted an answer that is relevant to this question:  MATH FINDS TOP CULPRIT AS LITHIUM-ION BATTERIES AGE

Just leave it plugged in over the month and you will be fine.