Here's a BIAB water volume calculator
that was created by another HBT member that may help you.
As far as that recipe you listed, I've brewed it twice using BIAB and I brewed each batch with 7.5 gals of water to start out with and my ending volume was 5.5 gals. Don't use the rice hulls in this or any other BIAB recipe because they aren't necessary for BIAB and will only make extracting wort from the grain much harder for you.
As far as the efficiency issue, I suggest using 1-pound more of the base malt to begin with until you get a feel for BIAB and get your process dialed in and your efficiency issues worked out. I no longer need to use any extra grain with my BIAB batches because I get at least 75-percent by milling the grain twice (or on an extra fine setting), stirring well, and performing a mashout.
Good luck with your first BIAB!