I'll give you an overview. I basically experimented in a creative world first to get it working, then worked out the resource cost in my real game world.
Get a Cart Assembler made first. This is your crafting table for carts. All the different components are put together here, along with coal to power it. Takes around 12 minutes to assemble to cart.
Components you need for the cart are a Wood Cutter (most expensive), Coal Engine and Internal Storage.
Blocks you need are a Cargo Manager, an advanced detector rail, and rail track. Place the detector rail next to the cargo manager, and make a note of which colour face of the Cargo Manager is touching the detector rail.
In the GUI of the cargo manager click the little square box with the multi-colours in it to switch the icon background to the colour of the face touching the cargo manager.
Clicking the icon switching between different parts of the cart.
Clicking the arrow changes the direction of flow.
The CM interface allows you to set up to 4 processes, that occur from top left to bottom right. Once the bottom right has been processed, the cargo manager releases the cart and sends it on it.s way.
First thing to set is the chest icon, representing the cargo space. Change the arrow to point at the cargo manager. This tells the CM to unload all the inventory of the cart into the manager.
Next, set the top right icon to the tree, representing saplings. Make sure the arrow points to the cart. This forces the cargo manager to fill up the cart with all available saplings. The cart can hold 3 stacks.
Lastly, set one of the remaining bottom two to engine, pointing to the cart. The cargo manager will fill the cart with fuel, which will be the logs the cart has harvested.
Then all you need to do is work out a system for pulling out the excess materials from the cargo manager to your sorting system.
I posted about it here
http://forum.feed-the-beast.com/threads/help-how-to-get-started-with-steves-carts.8736/ along with a final screenshot of my setup.