Thanks! So, just so I'm reading this right, it looks like the pH level is 9.7 so if I'm going to get into all-grain I should be looking to reduce that, correct? Or would it make sense to get something like 5.2 Mash Stabilizer and not worry about additions and testing, etc.? I'm trying to research out the nuances and finer points of the brew day.
No, it would not make sense to use 5.2 Mash Stabilizer. It almost never does. 5.2 Mash Stabilizer is likely an excessive addition of several minerals for the beer you are brewing, and is probably worse than doing nothing. Since you are starting from what is essentially a blank slate, it's easier to build your water the way you want it, using something like bru'n'water. There's enough information in the MWRA report that you don't need a water test for simple pH correction and rough profile alteration for the character of the beer.
Last time I checked (when I last brewed with it before I moved house last year), MWRA water has a high pH, but almost no minerals and low alkalinity. From the water report linked above, alkalinity is currently pretty low at 40ppm in the Metro-Boston system, and very low at 4.2 ppm in the CVA system. It's alkalinity you have to work against to reduce mash pH. Since alkalinity is low, it doesn't take much to reduce the mash pH to acceptable levels with MWRA water.
Playing about with bru'n'water on the Boston 40ppm alkalinity water, adding 0.6-0.8 ml/gal of 88% lactic acid to your mash water will bring 10lb of base grain mashed in 3-5 gallons of strike water to a room temperature mash pH of 5.3-5.4. If you have 1 lb of crystal/caramel malt around 40-80 L in color with that base grain, you can use 0.4-0.6 ml/gal of 88% lactic acid and get a mash pH of 5.3-5.4. 5.2-5.5 is the acceptable target range you are going for.
You also want to add a tiny amount of lactic acid to your sparge water - 0.05 ml to 5 gallons! (0.1 ml would be OK). And you should use 1/4 campden tablet per 5 gallons of water in both strike and sparge water, as the MWRA system uses chloramine as a disinfectant.
None of this includes any mineral additions to enhance the character of your beer. If you want to do this (i.e. adding sulfate for an IPA), then play with bru'n'water to get something like a suitable profile with mineral additions. You don't need to get anything exact - within 20% on the concentrations is fine. Then you need to check your mash pH again, with your actual grain bill included. It really doesn't take much to do this with bru'n'water or similar.
ETA. You might want to read the "brewing with low alkalinity water" thread in the brew science forum. You can add salts to hit the mineral profile for your beer without affecting the mash pH by adding the salts to the boil rather than the mash.
