If you are working off-grid on this project, I would look at doing most of the work with a tablesaw- faster cutting speed with less amp draw for cutting the large stuff.
I would get a good dado head and mill each board with 3 passes- one for the grove, and two for the tongue. This also will help to reduce the tearout that a large shaper cutter could produce with that much material removed in one pass.
If it was possible, I would make a shiplap joint on the stock, only requiring 2 passes, and the material would still have most of the structural integrity that a tongue and groove would have.
Charles
