1. When using 3% acidulated malt, does this replace an equal amount of the pils malt? Or is it in addition to the full amount of pils malt….
well, yeah, cause then you'd have 103% of the grist
you'll get gravity out of the acid malt, so it should be 97% pils/3% acid malt.
2. Do I modify all my water with gypsum (mash and sparge) or just the water that will be used for mashing? And do I add the gypsum to the water, or to the mash… (I already mash at 2.0 qts/lbs)
IMO, add to the mash.
3. On some of these online water calculators, it seems like if I add the gypsum you recommend to a mix of 50/50 distilled water and my water, it bumps the sulfates up a lot too, is this a problem?
you want the sulfates high to accentuate the hop character a bit.
edit - actually, how is that possible that adding distilled bumps up a salt - explain a bit here
4. Side question: will this water also work for a Bitburger-style German Pils??
higher carbonates in Bitburger - that's one of the key differentiating factors over Bo-pils
5. And a final side issue: any hints on the diacetyl question… what beer (or what food product) tastes like diacetyl?
the butter in movie/microwave popcorn.