Last time I made a good Czech pils I used the promash water profile for Pilzn and added a percentage of distilled water to my well water to match it as closely as possible. Turns out I can get close with 2/3 distilled water to 1/3 well water. If you have a water report on your brewing water you could try calculating that.
Does that give you enough calcium, etc for yeast health? That profile doesn't have much of anything in it....
And when folks talk of using "enough acidulated malt" what does that mean? I am comfortable in BrunWater; should I just add acidulated malt in the malt bill until the projected mash pH drops to something like 5.3?
Red, Weyermann's rule of thumb is 1% acidulated malt will drop the pH 0.1. That said, they did not say for what water alkalinity. For RO you would not need much, as there is no buffering from the water alkalinity.
The last BoPils was RO, 35 ppm Ca via CaCl2, and a triple decoction which has an acid rest. You can avoid the acid rest with acidulated malt, or adding acid to the mash.