I like the historical concept. I think it would be a great game. I think it would take four or five years to complete and then you should plan on about another year for beta testing. And that would hinge on having a competent team to work with you til the end.
But...if this is your first game using GameStudio, why not start by creating the models, terrain and code for one battle. Ignore the strategy and economic stuff. Just code the tactics and see how the battle goes.
That will give you an idea of the problems to be encountered and may change your game concept.
In game development I recommend "Dream big, start small."
