Looks like a really good breakfast stout! The only change I would suggest is to add the coffee at bottling instead of in the secondary if you want the flavor crisp and pronounced. In secondary it tends to get muted and stale, like day old coffee if you've ever had it.
I've done 14 lbs of grain in my 10 gallon Igloo beverage cooler without any issues (an Imperial IPA I have conditioning right now). I also made my own false bottom for it, which you can see here
(the 10-gallon version is the set towards the bottom of the OP). I use this cooler
and this pan
, though the cooler was much cheaper when I purchased it from Amazon.
Some sporting goods places and discount stores like Big Lots usually have the coolers a lot cheaper as well, so it's just a matter of bargain hunting. I really like my mash tun, though and have had zero issues with stuck sparges, even when I did a wheat stout and forgot to throw in rice hulls to help with lautering.
The recipe looks great and it should make for a tasty brew.