Wow! Starting out with a big one!
To get any kind of decent efficiency with a grain bill this large, you're going to have to sparge more and boil longer than you normally would.
What size kettle do you have? If you do a 90 min boil, you'll need to start with ~ 7.5 gals, if 120 mins, then ~ 8.25 gals. If you're pot's not that big, then you'll need to collect the extra wort in a bucket and add it to the kettle as you have room.
Another suggestion I have is get a demo of Beersmith to play around with strike temps and volumes. Shoot for a water/grain ratio of around 1.25. Use a single infusion mash schedule to make things simple for you.