Deep litter is the way to go for me! I don't know how well it would work with just straw, can the girls stir it themselves? You may have to help them.
Plan on a foot of bedding ultimately. Throw some scratch in everyday and they will turn it for you so you won't have to. If it gets packed under the roosts, you might loosen that with a fork or shovel on occasion to help them turn it.
Add bedding anytime you open the door and smell an unpleasant odor. Once you get to a certain depth, this won't happen anymore.
I would put a layer of sawdust or shavings in just to absorb at the bottom. Then you should be fine for the year with the straw. If you throw it on top of the straw, it will work it's way in.
I just take out a wheelbarrow or two of stuff under the roosts about every three months or so. I have 17 chickens now in a 3x12 coop, but they free-range all day on two acres, fenced. I let the poop build up in the winter under the roosts (they turn it, it doesn't stink, just gets deep) so heat will build up from the composting. It gets cold here in New England in the winter.
I never clean it to the ground. I would if I had disease, but haven't had to.
I put in lots of dry leaves this fall, about three feet broke down nicely. I used only one bag of shavings in 2008. When I go in to get eggs, etc, there is really no visible poop that I am stepping in. Just under the roosts.
Experiment and see what works for you, above all, have fun!