I definitely plant to dose phosphorus and iron because I think my plants will benefit from them since they are macros.
Iron is considered a micronutrient.
However, trace is micro only version of comp, will it benefit my plants if I use this with comp or will it not make a difference?
Flourish (comprehensive) is a trace mix with small amounts of macronutrients.
Flourish Trace is just a trace mix.
If you are already dosing macronutrients via Seachem Nitrogen, Phosphorus and Potassium, then while Flourish (comprehensive) is fine, you could just use Flourish Trace (this could be important if one is cheaper than the other).