Congrats!, As everyone has stated go with the Crew Cab, I have 3 boys spaced 3 years apart, just right for one getting out of the rear facing seat and for the next to go in. The ONLY way they fit in my 98 F150 extended cab is the rear facing seat in the center of the backseat. This keep the head area of the baby seat between the back of the driver and passenger seats and over the armrest. The rear facing baby seat would not fit behind the back of the driver or passenger seats, with out the seat being straight up and down and moved all the way forward. So with twins its not going to work for you, unless you put one up front. (Yes in a truck one can ride up front, IF YOU CAN TURN THE
AIR BAG OFF!)
As far as a brush guard it all depends on what you buy. Brush guards are just that, and will fold in and crush the front grill. It may save the mechanic behind the grill, just depends on the hit. But will still come with a warning of how it could cause you air bags not to function properly.
I have one on my truck its big and beefy polished stainless tube steel but the brackets would fold up in a second. Oh, yeah I have hit 3 deer in my life, one in my car, before having the truck, one with one of our fire trucks (3000 gal Tanker), and the last one in my truck. Well actually the deer hit me, it ran right in to the rear tire and bed of my truck, then I hit it with my sled trailer. Trailer was fine truck need some plastic repair the tire took the big hit. But the Brush GUARD looked nice and shinny! Just like RADSRH said above.
I have seen the push bar brush guards fold up also. Unless you are thinking a full bumper and guard combo, the brush guards are more for looks.
Well I was hoping more people would give their 2 cents here about undercoating because I will be looking at the new F150 Crew myself shortly.
Are you parking inside?
I noticed that my rust on my 98 seemed to increase big time about 4 years ago. 5 years ago on Nov 23 I bought the wife a new car. Guess who's went outside, granted it was 10yrs old with about 115000 miles on it, but I think the truck liked the heated garage. I know I will keep my next one just as long but I also know the 12yr mark meant repairs, lots of little stuff. some rusty parts just gave way. I joke it will be a new truck part wise before I sell it!
Oh forgot not sure if they work or not but each time I hit a deer I did not have deer whistles on the car. I have had many of times since then when deer have stopped by the edge of the road since having the deer whistles on all my cars now. State Farm use to give these out free
http://deerwhistle.com/ nice and small, easy to hide compared to the bigger ones in most stores.
Good Luck!