Here's some good information on barrel preparation, cleaning, and storage.
http://www.boomchugalug.com/barrel_instructions.htm
As for using the barrel, it's all about experimentation. Different toast levels will give you different flavors. Are you looking for used bourbon or wine barrels? Or are you starting with a new barrel? New barrels can be soaked in whiskey for a few weeks, but it's expensive to buy enough whiskey to do it (around 6 handles of whiskey).
I bought a 5 gallon barrel a few years ago and after doing 3 batches in it, I decided to stash it away. I'm currently storing it dry, but I'm hoping that re-hydrating it will bring it back to it's former state without issues. I just didn't enjoy all the work that came along with the barrel, but it's nice every once in awhile to do something special.
With a new barrel, a week is all that's really needed to give you an overpowering oak flavor. My first batch took 6 months of conditioning before the oak had faded enough to be drinkable. My second batch sat in it for three weeks, and it was still pretty oaky, but not quite as bad.
The third batch is when I started to notice the great flavors that you'd expect from a barrel aged beer. I aged it in the oak for 8 weeks, and it turned out fantastic. Just enough oak that you knew it was there. I think that the more I used the barrel, the less flavor it gave off. I also feel like the oak hits a peak after a few weeks. I tasted the third batch about 4 weeks in, and didn't notice much of a change between 4 and 8 weeks.
Hopefully this is the kind of info you're looking for.
