Yes, your pH test kit will be reasonably accurate for practical purposes if you can distinguish the colors well. Nitrate is a good number to know for plants: it should not be zero, but it should not be too high for fish. Ammonia and nitrites should be zero.
Flourish is a great fert and I use it, but I also dose phosphate, nitrogen, and iron by themselves as Left C mentioned. I like Prime because it is super concentrated, but all dechlors work about the same.
Don't think in terms of "I need more chemicals to make this work." Instead, think in terms of, "I need more answers to make this work."
I don't like running CO2 into my filter because I am afraid the CO2 will back up and I have to "burp" the filter a lot. Wooden airstones make very fine bubbles: I run one into a powerhead and it works great! But that tank is filterless. Plenty of people run their CO2 into their filter and it's fine. Maybe depends on the filter and the CO2 levels desired. 30 ppm is a good number to shoot for.
Left C's Seachem dosing calculator is great! I used it on all my tanks and then tweaked it for their individual needs. Funny how you can treat all your tanks the same and they are all different!
Meanwhile, read, read, read. Pick a dosing plan that suits your interests and your lifestyle, and stick with it for a few months before switching. Obtain fail-safe plants like Java fern and Anubias and common Crypts. PM me your address and I will send you some Java fern and crypts for $5 postage!