I use the Montessori 'Great Stories' (in a modified form) as our 'spine'. We are just starting, but the plan is to revisit them every year and then allow my children to go off on any tangent they like from there. Then there is no chasing down resources we might not use, nor is it completely 'bitsy'.

http://www.moteaco.com/albums.html

We also use the continents approach with geography.

I like the way this allows us to continue to revisit areas again and again, exploring a different part of it each time and building upon our understanding. IMO a four year cycle is too long for children this young, each year is going to work better for them.