Yes, PH the water first, the nutes won't effect it enough to make a difference. It's also kind of why you lower the PH so much, so that it over-rides the nutes.
Generally you don't want to adjust PH AFTER you add you nutes, I forget the reason why exactly but I think it has to do with nutrient lock out. I just never have done it so I don't know.
The way I have my stuff set up, it's all just automatic, I don't even worry about the PH, like I said I test once a year and it's always been the same since I moved here 5 years ago.