This all is looking really great bracer
The temptation to improve the 3D models is always there, but the core of the game is what should soak the most available time, you could later get help from other 3D artists to improve or add 3D stuff but coding is better done by a single hand.
Speaking of, have you thought about asking some of the usual SH3 modders for permissions to use their work? Many have created ships (merchant and war) and airplanes from scratch, not copyrighted stuff, and they would maybe allow you to use it. Would save you a ton of work.
Looking forward to the implementation of the map, it would be awesome in CIC style as a map/plot table where you could superimpose tools, general for map drawing and for plotting and even calculating firing solutions.
Limiting the starting available world to Norway and the arctic sea would be more than enough for a great campaign raiding the Murmansk convoys.