The overwhelmed feeling is your brain on overload. It's hard to start a large project such as this one you describe, not only because it is complex, and there is actually not enough room for storage, but because it is overwhelming. Many details.

I suggest that, to save your sanity, you attempt to break this whole process down into stages that are more "bite-sized" and will in completion lend you some encouragement to continue on to the next stage. Since I don't know all of what you're doing, I have no detailed advice, but this generally is what works for me when I tackle things like my closet, which is not only clothing storage, but craft supplies, archive for non-attic things, gift hiding place, gift-wrapping supplies area, and art and photo storage. It too is too small for all this.

(Some day I will conquer run-on sentence disease without a lot of editing...)

For instance, re the lost chocolates: it is a good idea to prioritize so that this sort of thing cannot in good conscience happen again. Such objects need to be in your way while still safe from rodent attentions - so that you must deal with them in a timely manner. :) I remember a lot of time sensitive things by putting them in my way.