Sam and I have opened a book on how long before you are an atheist. I say within 6 months as you are a bright guy who moves fast and isn't scared of change :-)
I'm with Paul
And I''d therefore forget about DAing yourself. I'm not DAed, definitely involved in "wrong doing", and never look over my shoulder. One benefit is that other flakey JWs can still contact you before they've made the final break which would be harder for them if you DA.
Intrigued by the Alpha choice. I've visited them and it had the feel of the JWs all over it - but then I'm a non believer and so my perspective is quite different from yours. We've got a newish church here called Destiny that's real happy clappy and expansionist but I haven't manged to visit them yet.
Good luck!