Too few diagonal moves for my taste. And no hippogonal moves at all. Can any of the pieces jump?
What is the use of the fortresses? They don't offer any protection to the royal pieces against frontal attack, so I guess the players would just ignore them. You did not specify any promotion rules, so there is no need to guard the back rank.
The only-immobile-pieces rule overrules the stalemate rule?
Now let's talk about the pieces.
The Infantry moves and captures 1 square forward.
The Grenadier moves and captures 1 square vertically and horizontally.
The Cavalry moves and captures 1-4 squares in every direction.
The Artillery moves 1-2 squares vertically and horizontally, and can capture 2-4 squares vertically and horizontally.
The Warship moves and captures 1-3 squares vertically and horizontally.
The Fortress does not move, but can shoot 1-2 squares vertically and horizontally and 1 square diagonally without moving.
The Lieutenant does not move. And so does the General.
---RULES---
The Lieutenants have to be captured first before the General. If you capture the General before the Lieutenants, you lose.
Since this is played on a big board, the 50-move rule becomes the 69-move rule, and whoever makes the last move loses.
If you stalemate your opponent, you win.
In threefold repetition, the one who makes the last move loses.
If you capture a Lieutenant with a warship, you lose.
If the game ends with only Fortresses, Lieutenants or Generals, the game ends in a draw.
So that's the rules for Napoleonic Chess!