The equipment you are looking at will probably work but the carbon system will probably not do much for the iron.
Water fluctuations are very normal in many areas. You should design the equipment around the worst case water you get.
Iron at 1.5 ppm can be problematic.
See if Aquascince can recommend a different media that handle both iron and H2S. Carbon will do a fairly good job on the H2s. Maybe a manganese dioxide based media.
Otherwise, the good old Chlorine injector/contact tank, GAC, softener combo is always fairly easy to work with. The chlorine injection oxidizes the iron to make removal easy for the GAC bed.
I am not a fan of relying on the softener for iron removal. it works but it is highly inefficient.