Imperial Stout minus the roasted Barley. I am going for a super dark, thick, chewey, big beer. I have become a huge fan of the english crystal malts as well, I think this beer is going to be pretty darned good, I just have to get my yeast straightened out.
Then what's the "coffee malt"?? I took that as roasted barley, since that's the flavor you get when you use it as 3-10% of the grist. I'd drop the black malt and use more roasted barley. You could also probably reduce/drop the Extra Dark Crystal and just add another few ounces of chocolate malt...
I prefer to use less specialty grains in my brews, but still get complex flavors. I think you could also reduce the different types, and tweak the amounts, and still get your target.
Or, brew this one, but brew it again with a less complicated malt bill and compare them.
I wouldn't mash overnight though, since I've read how people have done that and it turns it sour... A 90 minute mash should be plenty of time. You might want to mash a bit higher than 150 though, like 152-154 to increase the mouthfeel/body of the brew... A bit of flaked barley could also go a long way to helping there (even 1/2#)...
BTW, you're beyond the color range for an Imperial Stout... As it stands, you're at ~54 SRM, where the style is 30-40... I don't think you'll be able to tell past someplace in the 30's though. I would tweak for flavors more than such dark color...
I do think that 1728 would be a solid yeast for this one...