I went and bought some liquid lactic acid, calcium chloride, and gypsum. I'm planning on brewing a Belgian Tripel next week, and I'll be adding about 4g (each) of the CaCl2 and the Gypsum, and 0.5 tsp of the lactic acid to the mash water. Hopefully that will get me to a nice pH of 5.4 (based on Bru'n Water and Brewer's Friend calculations).
Beyond my mineral/acid adjustments, I'll be implementing the updated cleaning/sanitizing methods discussed above to avoid any residual oxidizing agent entering the beer, as well as ensuring better sanitizing.
Another minor change I'll be making is to add flavor and aroma hop additions (in my previous 6 batches I have only used 60min bittering hops) to see if more malt-hop balance helps with my flavor profile.
Lastly, I will see what I can do to modulate fermentation temperature. For a tripel, it probably won't be quite as crucial to keep the temperature down, but I still might try the wet-towel+fan or water-bath method.
Thanks for all of the helpful feedback, everyone!