Years ago, I sealed up some surplus Hodgdon powder in plastic. Some of the wartime surplus powders would deteriorate and cause everything nearby to rust.
I used a sealer made for food preservation that did not use a vacuum.
I don't think sealing brass and bullets are necessary. They won't tarnish unless handled.
Powder and primers would benefit if you live in a humid climate.
You need to choose the plastic bags carefully. Most plastic bags are designed to fall apart after a few years
so they are 'green'.
Depends on what you mean by long term storage. If it's for something like a bug out kit and the cartridges are of exposed lead then it might help as lead does oxidize over very long periods. Other than that I really don't see a need for it.
I do have two long guns that belonged to my Mom and Dad that are vacuum sealed. Moms gun is a Stevens semi auto 22 rifle given to her back in the 40's and Dad's is a Remington 870 he got the first year they were produced....1957 or 58 I think. I don't shoot them and intend to pass them along someday so I oiled then down well and cut a bag to length and vacuum sealed them. Every couple years I snip the end of the bag and pull then out for a wipe down and then return them to the bag.
The trick is to preserve brass and various other metals whilst moisture out. While removing moisture is relatively easy by doing a bake oxide, increases in oxidation are not as easyto cope with. Higher oxidation caused byexposure to air for generations may later require the use of more active flux systems. In some instanceshaving a stronger flux is certainly not allowed. I bought a maxkon vacuum sealer from crazysales to seal the extra bullets too. And using normal food saver bad is enough to preserve them. The vacuum sealer can not only be used for food preservation, but solid metals.