Just a few comments
1. The reason why Medicare Part B isn't creditable coverage with Medicare is because when there are budget problems, the VA can modify those priority ratings for those of higher income, no service-connected illness or injury and manipulate them for those who aren't critical of their services and thus the VA health benefit isn't set in stone due to this budgetary influence.
It is a good idea, if and when possible, for those with VA health care to have Medicare Part B (and get it when 1st eligible to avoid the LEP) - that opens up many more providers to them if need be.
2. State insurance laws and regulations play a big part in how Medigap plans (Medicare Supplemental policies) function at the state level. Some states may have a time specific period where one can change their policy to an equal or lesser one without underwriting. Some states may open up all of the alphabet plans to those less than 65; others don't, or they may restrict them to just a couple of plans. Do they set the type of ratings these insurers use in their state? I don't know. Some national plans like AARP UHC use the same rate type all over the country, I believe, community rated, I think. However, calculations are still based on the area/state because health care cost do vary up and down even with Medicare.
You may want to review the rules of your state on Medicare Supplemental or Medigap plans at the state's DOI website just to make sure there isn't a rules condition there than could affect you and your plans.
3. I have always been under the impression that Community Rated is the rating type that would be the least volatile in premium increases just because the pool is large(r) and with a wider span of enrollees in age and therefore, in health status. I don't know of any specific analysis on the different rating types but for those which are based on age, especially attained-age, one should should expect larger increases later in life.
4. Yes, your VA Medication benefit is really good however, just remember that there may be some meds that aren't covered. The VA has its own formulary, all VA docs use this formulary, so if you are visiting a doc outside the VA system, make sure that doctor is also using that formulary to assure that any med they prescribe will be covered.
5. Waiting until the very last month of the initial enrollment period for Part B sounds like a good plan - just don't miss it - the late enrollment period premium penalty is pretty harsh and it last forever.
6. I am not sure that your plan to get a MA plan and then go back to Traditional Medicare with a Medigap plan is a good idea (the 12-month plan). Several things could throw a wrench in that plan. While you can always switch from traditional Medicare to a MA plan and then even back to traditional Medicare. However, a Medigap policy may not always be available to one, or at a non-underwritten price premium, once the initial enrollment period has passed. It is a bit risky and could use up any planned savings real quick.
Medicare.gov - When Can I Buy A Medigap Policy - Guaranteed Issue Rights
I think sitting down with a LOCAL, KNOWLEDGEABLE MEDICARE insurance broker who also understands the VA system would be worth its weight in gold to you - There is no cost to you for such a consult and they could always see something that you might be missing just in the various state rules or even another type fed/state benefit like the Medicare Savings Program, if you qualify.
Medicare is a program that has lots of twist and turns in eligiblity and timeline within their various programs - a trip up could be costly and it really takes knowing a lot about you personally to advise you on any specific - that's why I am suggesting sitting down with a LOCAL, KNOWLEDGEABLE, MEDICARE insurance broker for that consult. Yes, state DOI have people in the SHIP (State Health Insurance Program) to answer questions - maybe they would do but then again maybe not - depends on their knowledge - in your case, Medicare and VA.
It's Always Something . . . . Roseanna Roseannadanna