Humble Bundle question

It varies on bundle to bundle basis - so you gotta check or ask about a specific bundle. Some bundles give individual kesy for each game and DLCs, some give one keys for game+DLCs, and some give a single key for the whole tier.

Generally yes but It depends on the bundle.

For example, the Borderlands bundle has one Steam key for each tier so you can't gift just a base game or DLC.
The current weekly, on the other hand, has individual Steam keys for each game.

Muchas gracias, everyone.