Welcome MzPen!!
So nice to see you here!
Well...what I would suggest doing first (other than reading the book!) is checking out the 'sticky' on the top of this forum called "Basic BFL Information" (or words to that effect

). Most of us chicks here also lurk/post at
www.leanandstrong.com - which is a GREAT resource of info (I'd suggest lurking for awhile first - if you're accustomed to the easygoing pace of 3FC, the speed at which L&S moves can be a bit overwhelming at first!). Another great thing to do would be to skim through the old BFL/BB threads...you can glean some great info there.
As to the bodyfat measurements...you can get 'em but it's not required. (IMO they're pretty arbitrary anyway). I would suggest that on day 1 or maybe 1-2 days before your challenge, you take some before photos (front/back/side), tape measurements (calf/thigh/hip/waist/chest/bicep) and if you must, weigh yourself...(as you can see by my signature, I don't put a whole lotta faith in the scale) then tuck all that data away for a few weeks. And for goodness' sake, do your best to stay OFF the scale for at least the first four weeks - BFL is NOT a 'quick weight loss' program, and a lotta newbies have been HIGHLY discouraged by the scale, especially early on. The Pants-O-Meter is definitely the BEST way to go here!
Once again, welcome and please feel free to ask any questions!