Thats going to be a tough one to pull off with a toolkit.
Your also going to have to write some really endearing characters, and then kill them off in a way that dosnt make it look like you just did it to drive the story along.
The whole war is hell with no solution also makes for a depressing game. One of the reasons than BoB worked so well is that it was essentially a flashback.
Which is an approach you can use while still keeping the character completely player created although it will require an intro and some creative story telling.
On the subject of intro's. One of the key things about war is that you need some sort of ideal. Just throwing a character into a war without anything to fight for would be pretty empty and you wouldnt get that feeling of something worth fighting for and dying for. Of course finding out that what you are fighting for isnt quite what you thought it was, well thats a great way of having a non character dependent twist.
The new Bards Tale game does something similiar and it works really well, whether or not you piece the clues together before the event. Because in the end it never limits your ultimate choices.
The other big challenge is going to be making a battlefield. One that actually looks like a battlefield, rather than just wave after wave of spawns.
Best of luck with it. But in my experience it's better to get your hands on the toolkit and see what it can do before making grand plans.