I been tinkering with water chemistry the past 6 month or so myself and I started like you with getting a copy of the water report from my county and entering it all into the Bru'N'Water spreadsheets. I've learned a lot but still feel I'm just tossing in chemicals according to what the spreadsheet is telling me. I'm sorry I don't have answers for you and I just have more questions to toss in here.
I decided to take a step backwards and focus just on pH only for now. I plan on purchasing a pH meter from the great recommendations I find here. I read a ton of information out there on mash pH and how to adjust it but still a little unclear on the exact procedure. This is my guess for checking and adjusting my mash pH once I have my meter.
1. Measure the pH of my tap water. (not sure how accurate the public water reports can be)
2. Enter the information into some brewing software along with the ingredients. See where the mash pH will end up without adjustment. Use the recommended treatment from the brewing software to hit my projected target mash pH.
3. Treat the mash water prior to adding grains?
4. Mash in, take a reading to see if you hit your target.
5. Take notes for the next brew. Rinse and repeat on next batch.
If you don't have a meter, I assume you can simply use the pH reading on your report and then trust the brewing software that you will hit your target if you make the right additions?
I read that pH meters don't last all that long either, maybe a year for a halfway decent one. I'm also assuming that if I spend a year recording all my batches, I really shouldn't need a meter anymore unless something drastically changed with the local water supply. I'm hoping someone could shed more light here and steer us in the right direction.