Not a popular opinion around here, but fussing with minor changes to your salt additions is not going to make or break this beer. In fact, it will make almost no perceptible difference. You're going to get plenty of minerals from the malt once the grain has been mashed - including chloride, sulfate, magnesium, potassium, etc.
All you really need to do for this beer is to start with a Cl- : SO42- ratio of about 2:1, aiming for about 150ppm chloride. With RO water and relatively small additions of calcium salts, you'll probably be right around pH 5.4...so I don't get the need for extra alkalinity. Add it after you're first pH reading if you're too low. Conversely, add some lactic if you're too high.
Concentrate on technique and keeping oxygen to a minimum after fermentation, and you'll have a great beer.