(which of the various pony threads to post on?

)
Have just added a (sideslung) 3L pony to my setup (15L main). Currently have three second stages and was considering getting rid of the octo on the main cylinder - but I think I'm persuaded by the arguments above. If I've got it, I might as well take it with me - it's no use in the kit box, if I have an incident under the water!
I'm now thinking of going over to the long hose primary/ necklaced octo setup.
Questions:
(1) Which octo do I necklace?
(2) Where do I stow the other one?