Your model is looking good so far. I would most likely model the whole plane as a whole, and then break it up as desired when it came time to refine everything. That way you know everything is going to line up.
i'd take a look at some actual photo references for this plane only to see if they put the parts together with rivets or welding... rivets on the body would look cool and could probably be applied with a bump, although modeling them would look pretty cool in the pre-texturing phase and after as well.
i agree about the propeller blades not looking right, but can't really place what it is about them. cockpit and rear wing look pretty good.
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