Where to begin! This is something I have looked into a lot on my own, that video of the Mixologist is a great start for this topic.
I have/do use systems that automatically dose nutrients like the Grobot Evo: https://hydrofarm.com/downloads/fc/GroBot_Evo_Manual_11218.pdf
There tend to be a few things that always end up going wrong.
1. Tubing either breaks/gets clogged. Remember, lots of these nutrients build up deposits over time.
2. Nutrients also have shelf-lifes that change based upon when they are combined.
3. Different plants need different solutions, this means you are left with two options. Having a "mixing tank" where the nutrients are combined, and then sent to the end destination reservoir. Or, you have to have multiple dosing/monitoring systems. This requires multiple sensors, and actuators thus raising price.
4. All liquid nutrients recommend "shaking" prior to use, this is a necessary part of the process, that if you just pump nutrients from the bottom of a solution that has settled will give you incorrect doses.
I have tested solutions using an IV drip, this is a good start, when sourcing the pricing though, if peristaltic pumps can be obtained for $5-10 each, they really are the best solution using moving parts. I am currently working on a nutrient dosing module that will run using only one pump. MIT appears to have a similar solution using the Dosatron. Let me know if you'd like more information regarding what I'm working on.
To answer the original question though regarding sourcing raw nutrients, I wish I knew more about chemistry to answer you, I would be very curious though to know what you find out. The best answer I have though if you want to make a self-sustaining system is to look into aquaponics.