I have all the Seachem line. I dose Iron very rarely if I see yellowish leaves. Same goes for potassium. You need to buy just Seachem Flourish comprehensive for you nana. No need to buy any other fertz in my opinion.
If you don't have co2 then you can use flourish excel as a substitute for co2 injection but that is also your choice. Be warned excel has algacide properties so if you want to keep algae for your pleco then don't use excel.
Flourish name is confusing. Don't pay attention to the word flourish itself. Just pay attention to the word which comes after the word flourish.
Flourish Excel: As a substitute to co2
Flourish comprehensive: combination of all necessary fertilisers (You need this)
Flourish Iron: Contains Iron for plants
Flourish Potassium: contains potassium
And so on.
You can watch this very informative video about potassium and iron and how often use them. I never used other fertz like phosphorus etc and my plants never had any issues.
My dosing schedule is:
Flourish comprehensive Saturday
Flourishing Iron (very little) Tuesday
Flourish Potassium Tuesday
And repeat this and plants are lush green always with strong leaves and no yellow or damaged leaves at all. Seachem line is the best.
Hope this helps.