Re: flash. What's your camera? If you have one with an integrated speedlight transmitter, being able to use a 430 off-camera could be a huge plus. (the 270 II can do this as well, but I believe the original 270 could not). Plus canon has refurbs available, which I'm a huge proponent of, since they're cheaper and individually inspected before leaving the factory. Anyway. Between the flexibility of off-camera flash, and having a rotating head, you'll be able to do a lot of fun things with light.
Otherwise, if you have a model you know well, and you're a relaxed and easygoing person, then I think that while planning is valuable, you should trust your spur-of-the-moment instincts as well. Either you or your models may see a particular spot, or envision a particular pose, and even if it's not on your planned list, go for it! Worst thing that could happen is it doesn't work out as great as you thought, and you can move on to the next planned out spot. But if you know some places that you have in mind, and they have some places they have in mind, I'm sure you'll be able to capture some great images!