Edward Veira, a Constitutional scholar, wrote a pretty good book about what The Militia is all about. I haven't finished it yet but it has lots of good info.
(Has a picture of the Porcupine Flag on the front cover.)
Congress is charged to provide for organizing, arming, and disciplining The Militia. (They've never really done this. )
And there are words in the Constitution about "the Militia of the several states" implying that it is normal and expected that the States would have their own Militias. And there are words about the Militia being called forth to enforce the laws of the union, suppress rebellion and so forth.
All this to say that Veira's view, supported by extensive citation, is that the Militia is an instrument of each State. Citizens are armed in order that when they are called to serve in the Militia that they bring their weapons with them.
(The Swiss model works pretty well to show what ought to be in place.)
If you could convince your state to authorize your group as part of the State Militia then you would have a completely Constitutional activity. The Militia is an agency of each State. ("the Militia of the Several States")
A self-selected group of armed citizens holding maneuvers would not be well-treated by the media, the police, or the courts. How could anyone know if you're rehearsing for insurrection instead?