The ceiling insulation will be 1.5" of foil backed rigid foam, with a layer of reflectix between the foam boards and the bead-board that will be the finished ceiling. The foam is mounted with VHB.
Because of the window hassles, I've only done the first layer so far.
The layer is sealed with expanding foam.
The first layer is 1" thick board, the second will be half inch thick. I will also foam the edges of the second board.
There will be a layer of Reflectix after that, and then the actual birch bead-board ceiling. Power for ceiling can lights will run between the Reflectix and the 1/2" foam board, with adequate service loop wherever we end up mounting the lights. Determining that is something that will be done experimentally.