Thanks for all of the responses so far! With the future of resolution 42 in question with the combined residencies I wonder if the 5 hold out states that require AOA inter year will be able to keep me out since after the merger if I don't stay in the AOA. It'll be interesting to see how it plays out.
Who knows what the states will do with their AOA intern year requirement in the future with the merger. In the meanwhile, it would make sense to get Resolution 42 done just in case ... you never know how the future will turn out (and where you may ultimately end up practicing ... or if you join a group that does telemedicine that involves one of those states)
You only need to be an AOA member to do resolution 42. Once that is done, no need remain a member unless you want to
You don't need to be an AOA member to take COMLEX 3. I would suggest taking/completing the COMLEX series which will make you eligible for license in all US states/territories. If you take USMLE 3 but not COMLEX 3, you will be ineligible for licensure in certain states (California, Florida, etc) since they will not recognize your USMLE 3 for license purposes.
Unless you want to be AOA specialty boarded (instead of ABMS), you don't need AOA membership. Since you're doing an ACGME residency, no reason to pursue AOA board certification. In the past, this was a route some DOs who did ACGME residency but AOA fellowship would need to get AOA recognition of their residency (Resolution 56) in order to take the AOA board certifiation and AOA subspecialty certification. With the merger, likely a moot point.
Overall, no need for AOA membership beyond intern year, and only keep during intern year for Resolution 42 (not require, but I recommend because you never know what the future might bring)