Think in some countries it would go a long way...in the US not-so-much. The US isn't quite there yet culturally that people could accept that

In the U.S.? Not a chance! A candidate has to pretend to be 'religious', and have a 'nuclear' style family, in order to get elected. An attractive spouse, and 'cute' kids helps!

One could only hope but presented in the right manner it might just fly with all the negative stuff about the catholic church.

I think it could be a future possibility and I would venture to say even a certainty once third parties are viable and fully recognized and established entities in the United States.

As for the tax breaks for all nonprofits and charities. They would have to be audited regularly and only allowed a reasonable overhead. No profit no huge pay scale

Depends on the election and region and timing. In the US Presidential election Trump was a joke and huge underdog, but Clinton ran one of the worst campaigns in history and the Russian interference edged her out. He would have lost 99% of the races he ever would have been in.

Building an ideology around atheism alone is a huge mistake. Rejecting religion alone is not a a sufficient basis for either a moral code, or a political ideology.

For any success with this at all you would drop the word "atheist" in favor of agnostic.