Humming-

You can’t put more than one augment card on a single host creature. Once a host creature is augmented, the host part gets covered up and it’s no longer a host creature.

The creature card with augment isn’t put onto the battlefield until the ability resolves. This means if the host is destroyed, the creature with augment stays in your hand. You can’t choose a different host, but you can activate augment again if there’s another host available.

Augment can (and usually does) change the name, card types, subtypes, rules text, and power/toughness. The combined creature will have (at least) two artists and may now have multiple colors. Anything covered up in the augment process doesn’t count, so ignore things to the left of the “metal bar” in the art of host creatures.