A lot of stuff is subjective. For instance there are many people going to LEDs now, but in the winter, I need the heat from the HPS and could not grow with LED unless I also heated the room--rather a silly thing to do when I have the HPS. The cost of LEDs can be prohibitive, too. I looked at replacing my 1000W HPS this last summer, but did not have the $600 it would have taken. The same with nutrients. I know that some here get great results with products that I did not and vice versa. To some extent, you need to personalize your grow to your circumstances and growing style. For instance, I grow organic in the summer, but hydro in the winter because of my circumstances. I grow hydro in the winter because I have too much snow and not enough room to deal with organics and soil. Two different people could have identical grows in different places and they would probably turn out quite different. There is really no BEST of anything. No singular products that outshine the others. It is more an understanding of the basics and then fine tuning your grow to you. You can post your specific question here, like you did with the vermiculite/perlite thing.
pH down is acid and pH up is alkaline. Do not buy products to pH spas or pools, get some for plants.
I mostly use General Hydroponics products. I have tried a lot of things over the years, but like them best. For hydro I use their Flora Nova Grow for veg. I use the Lucas formula in flowering which is the GH Flora (no Nova) Micro and Bloom used in a 1-2 proportion. For organic growing, I use General Organics. Although I am generally not partial to products that have 6-8 parts, the GO Box is easy to use and very affordable and I have found that my plants like it better than some of the other organic nutrients I have tried like Roots, which was a 1 part nutrient. I also use their pH up and down and Azamax, an organic pesticide.
So, think about how YOU want to grow--what appeals to you? Get a basic idea down on paper and we can help you fine tune it. But ultimately, you are the one who is going to have to decide what is best for YOU. We will try and steer you away from bad and help with the good.