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When I make a libation, I'll either share the cup with the Gods, or pour one for myself and a separate offering for the god(s) in question. The portion of the offering for the Gods I pour out onto the earth, whenever possible.

I think if you're making an offering to the Gods, they definitely need a portion that's specifically theirs. I'm sort of caught in your wording - "For" implies that you're offering to these things, so you need to pour these out, not consume them entirely yourself. If you were looking for these things - Hearth, Blade, and Thor - to grant you their blessings and imbue your drinks, and then consume them, that's fine. But you'll need to tweak your wording a little.

I don't see the harm in blessing the food you buy - I often give thanks for the produce I buy, as well as blessing the food I make with it. However, make sure you have asked your housemates if it's acceptable to them as well - they may not want or appreciate the blessings of those outside their own beliefs.

It's up to you whom you choose for your blessings - so long as it's appropriate to ask those deities for such a thing. My own preference is to ask agricultural and hearth deities for blessings on food. The Gods each look to their own interests and influences. They don't expect us to call or offer to all of them all the time for everything. It's perfectly appropriate to honour one individually, even if we work with more members of the same pantheon. It's your choice as to whether to call one or all.
On the occasions where I do honour all the deities I work with, I do so by saying things like 'Gods of my Hearth', 'Shining Ones', etc.