By no means an expert but I have one first place for one of my meads (a gruit mead) at the Mazer Cup - so you can take anything I say with however many grains of salt you feel you want - but the key to good mead making is in making a successful traditional mead - honey, water, yeast and nutrients. There are no ingredients to hide flaws behind and the honey is front and center. When you can pull off a trad mead then the world is your oyster. Okay
Yeast: IMO you select the yeast for the characteristics they offer. Check out the spec sheets. I often choose beer yeasts because of what they don't do (US 05 is a clean fermenting yeast) or what they do provide (Belle Saison highlights peppery notes). Some wine yeasts such as D47 fermented at higher temperatures produce all kinds of esters which add to the complexity of the mead if I am making a very low ABV mead (6%). You don't want those esters? Don't use D47 and ferment at the lower end of the yeast's preferred temperature range.
Acid adjustments? I adjust acidity before I bottle based on how the mead tastes. That has nothing to do with pH (that is only relevant in terms of how well the mead might age and how much K-meta I need to add to inhibit oxidation and spoilage), and everything to do with TA. But TA is as much about taste as it is about any number although conventionally you want to aim for a TA around 6-7 g/L
Proper pH? That's like a proper accent (mine is Scottish (working class Glasgow) and I view it as very proper but it ain't Boston or Brooklyn or English "home counties"). IMO, the last thing you need to worry about - No, I take that back - it's the first thing AFTER the last thing - is the pH of your mead. Sure, honey has no chemical buffers to control pH so the pH can swing wildly - and drop precipitously - but the key idea is then that you refrain from adding anything acidic to the primary if you can avoid that and use the secondary to add fruits and spices etc. The alcohol always helps extract more flavors than water and the yeast in the primary can blow off much of the volatile flavor and aromatic molecules, so adding fruits and herbs and the like to the secondary is a win win. It's a bit of a myth that yeast curl up and die when the pH drops to about 3. They don't. But they may experience (unnecessary) stress. And stressed yeast pass that gift right back at you.
