I would think that vacuuming sealing would crush the cereals. Is there a specific reason you would be taking them out of the original plastic bag? Otherwise, I leave mine in the factory bags, making sure they are well sealed (gently squeeze a new bag, does it hold firm or leak a bit of air?).
You could empty all the boxes into a single mylar bag, seal it and toss into food-safe 5 gal bucket, add an oxygen absorber and then seal the lid on.
My kids always roll up the cereal bag and shove it bag down into the box. Then close the box with the preset tabs. I have quickly learned that this does not keep the cereal fresh for very long at all. The best thing to do is empty out the contents of the cereal into a storage sized ziplock bag, or a gallon sized air-tight tupperware.