You need a minimum of 3.5 gllons of water so you'd have a 1 qrt/lb.
How much you sparge will depend on how much dead space you have in your tun. If you wanted to do a no-sparge you'd have to add about 6.5 gallons of strike water (assuming the grain soaks up .1 gal/lb and your tun has .5 gal of dead space). You can divide that 6.5 gal up however you want between the strike and sparge.
With the Brett in that blend you may need to give it more time in secondary, keep an eye on the gravity and don't bottle until it is stable for a month.
Sounds like a good recipe, hope it turns out well. I did an Old Ale with Brett C and oak ~4 years ago, really complex, but the body was a bit too thin in my opinion. You might want to add some flaked rye or something to add body even if the FG drops low.