I measure my nutes through PPM.
I first measure the water base I will be adding my inputs to. Whatever the PPM of the water is what I subtract from my overall PPM. Thankfully, the water in my area usually doesn't exceed more than 80ppm. I only use 2 main inputs for the most part at any one time. Base nutrient and Cal/Mag. At key times in the growth stages I'll blend both my grow and bloom nutes. I don't use boosters or enhancers.
The only boosters or enhancers you could say I use are mycorrhizae and soil bacteria. The nutes I use already have enough sugar in them to feed the rhizosphere along with the extensive root system I develop exudating sugars to feed the rhizo so I don't bother buying bottles of liquid sugar like Bud Candy.
I use CaliMagic for my Cal/Mag and FloraNova for my nutes. I add the CaliMagic first, mix it in well then add my base. The first two weeks of seedling/sprout I use some Voodoo Juice along with a weak(300ppm) solution for the first couple of weeks to get the bacterial colony going but no Cal/Mag until after the first couple weeks. Once they're ready for their final home I dust the transplant hole with mycorrhizae and water the plant in.
After having worked at a few licensed grow ops, getting to watch the Master Grower test out products, I've come to the conclusion that most of the amendments they offer outside of base are not really applicable to tent growers. Production growers sure but the increases you get from amendments is minimal at best. 2% increase in dry weight is a big deal for a large production facility but worthless to a tent grower.
IMO, the key is in balancing your nutrient ratios correctly to the stage of growth the plant is in. This will minimize lockouts or slowdowns in growth.
As far as metering gear I use Bluelab meters but Apera makes some great meters also.