I was planning to brew this porter/brown ale next as my first BIAB and was wondering I should add a bit more pale chocolate, and any general thoughts on this recipe.
I can't comment on brown ale as I've never made one and I'm not familiar with the style - but I have made a few porters. It depends exactly what you mean by porter as there are different kinds... But if we're talking London/English/Brown Porter...
To my mind (others will justifiably disagree!) you'd be better using brown rather than amber malt as the flavour is really an interplay between brown and dark crystal malt, with a bit of chocolate malt to add colour and complexity.
In the GH book for his brown porter (excellent BTW) he uses about 13% brown, 10% dark crystal (the one I use is about 80L I think) and 4% chocolate malts - so you're maybe not a million miles off apart from the amber/brown malt thing, though I'm not s
Also excellent is a
Josh Weikert recipe which uses 10% each brown, dark crystal and chocolate rye malt (I'm tempted to up the brown and dark crystal to 15% next time as an experiment just to see).
So to answer your question - yes I think you could up the chocolate a bit of you want to, but equally your probably fine as you are. Use a recipe calculator to check the colour - 20 SRM or just over will be plenty dark enough, very dark brown to black with red highlights if you hold it up to the light.
I'd also like to try using both Nottingham and Windsor
Regarding yeast, in my English Porters I've used WY1056, S-04 and most recently CML Beoir (still conditioning!). I've never used Nottingham or Windsor so can't comment directly, but.....
I recently did a split batch ESB between CML Midland and Beoir - Midland is supposedly the same strain as Nottingham. Both were good, Midland attenuated a little more and was more bitter whereas Beoir was more malty. The latter is why I chose Beoir for the porter I have conditioning now.
Now I
believe Nottingham is quite a high attenuator - I suspect either (or both) or your yeasts will make a fine beer but I wonder if Nottingham might end up a bit drier? I might be inclined to look for a yeast that attenuates a little less and/or accentuates the malt a little more - but like I say I can't speak from experience with Notty. I don't know enough about Windsor to know if it fits the bill here.
But if I read you right you're planning a split batch between Notty and Windsor, in which case I'd say go ahead - I've only done a split batch a couple of times but I kinda wish I'd do it more as it's the easiest way to experiment (compared to malt, hops or water) and the results are usually really interesting.
Good luck,
Matt