Four plans. Pay for the months you need, not all twelve.
Work on a plan while you are making video. When you stop, park all your files in Deep Storage and step down. They come straight back into the editor when you are ready. Working all year? Pay yearly and save.
Questions
The reason to be here rather than on a storage bucket: you can step off a working plan with your files intact, and step back on.
You finish the season on a working plan, move your files into Deep Storage, and drop to Basic until the next one starts. Three or four working months a year costs you three or four working months, not twelve. The library is still yours, still listed, and comes back into the editor when you want it.
It is genuinely cold. The included retrieval takes up to 48 hours. That is the trade that makes it cheap. A faster retrieval of about 12 hours can be chosen and costs extra. If you need something the same day, it belongs in Archive rather than Vault.
One copy out per term. A term includes one restore of your Deep Storage content back into My Files, where it arrives viewer and all, ready to edit. Further copies out are sold separately.
Downloading to your own machine is counted in gigabytes, not files. A term includes up to one full copy of what you are actually storing, however many files that is and however often you fetch each one. Store less than you bought and the allowance is smaller to match. Past it, downloading draws on your plan's monthly allowance, which you can top up.
It is prepaid for a fixed term. The terms it is sold for are stated on the Deep Storage band above.
You are billed on what lands in Deep Storage. A video takes its viewer copy with it, so it can come back ready to edit rather than being rebuilt. That copy measures about 17% on top of the original file, and it counts toward what you are storing.
If you only need more of one thing, buy more of that one thing. Each one is offered on your Usage page, under the meter it refills, once you are signed in. Past two or three add-ons the next plan up is usually cheaper for more, so it is worth comparing the totals before stacking another one.