I have recently started brewing with R/O water using the same spreadsheet. I second not adding any baking soda. I add small amounts of Epsom salts like you have listed and similar amounts of Gypsum and CaCl2. If I need to bring my PH down I add acidulated malt to to the mash. So far my beers have come out very good but I still need to get a Ph meter to make sure things are truly in line.