No stashing, only what's in your backpack. I'll edit the OP to make that clearer.
Follow the guidelines of create character, logout, set MP10, go. Also will add in OP.
I've been trying to figure out a way to remove the additional characters from the ladder. I'll have to try and contact the ladder support staff to see if we can only add specific characters and not an entire account or remove the undesired ones. Sorry for the confusion on that part. At the very least, we can track everyone's progress using that and then create a leaderboard table using the information from there here in this thread.
It takes some careful planning and prep to make sure you have some back up stuff in your stash.