Congrats on your huge BTC surplus!
To make the biggest difference, consider looking into Effective Altruism (an idea, not a charity) if you haven't already. Their motto is “using reason and evidence to do the most good”.
Perhaps do away with the charity proposal form, and instead choose one or several of the most effective charities as ranked by GiveWell.org (who do rigorous effectiveness analysis). OpenPhilanthropy is a charity that takes the EA perspective.
Unfortunately, seemingly worthy charities are often orders of magnitude less effective than the few most effective causes. Charity evaluators like GiveWell help us find the gems that can leverage our money many times more effectively.
For more info about Effective Altruism, listen to Tim Ferriss and Sam Harris interview the co-founder of Effective Altruism, check out this NYT piece, or read Doing Good Better.
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