Which flakes are gluten free?
Quinoa, buckwheat and rice flakes are naturally gluten free. Oats are a separate question, as they are usually processed alongside wheat – check the individual pack.
Do whole grains need soaking?
Most benefit from it. A few hours in cold water shortens the cooking time noticeably and many people find them easier to digest that way.
Is organic worth paying for on grains?
That is your call. What certification gives you is a documented standard for how it was grown, rather than a claim on the front of a box.
How should I store them?
Airtight, cool and out of the light. Wholegrain flakes and flours contain natural oils that go stale over time, so buy a size you will actually get through.