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.
Net