I did a Smoked Porter PM with a very similar recipe. I used about 10% smoked malt which gave it a really nice smokey flavor without dominating. 18% smoked will punch up the smokey flavor, but it's really your preference. I noticed that the smoke mellows out with time.
Regarding the mash, I just mashed the smoked malt with the specialty grains (no 2 row) and it converted fine. I mashed at 154 and got a little more body than I wanted. The next time I will mash around 152. If you follow the 1.5 qts/lb guideline, you should use around 6 qts of water in your mash. I am just starting out with PM and use a 2 pot on the stove method. I sparged with 2 gallons of water at 168. Not sure about how you would sparge with 2 cups of water?
I can't be of any help with the Special B as I have never used it.
Bottled: Yuengling clone, Hoppy Pilgrim IPA, Janet's Brown, Bourbon Smoked Porter
On Deck: Pale Ale