I actually ordered FoB over the weekend. The dwarf in my game wants to go for the classic 'refound anscenstral home' thing. In addition, my party somewhat dislikes the leadership of their home town and I figured this would be a good way to give them some control. I doubt they will want to get into the numbers, but I can alteast translate their general actions into game terms and generate some (hopefully) consistent effects.
As for Cry Havoc, I have it and like it. Given that FoB works at a more abstract 100 per unit scale, I'll probably use Cry Havoc for the under 100 combat. It is crunchy enough that I think it would simulate the hordes of low hd beasties combat pretty well, allowing me to award xp and treasure normally.