The only major problem with traces and macros is that iron and phosphates will combine to make a precipitate. If you tried to premix all of the ferts in a bottle of water for easy dosing, most of the iron would be at the bottom of the bottle as a solid powder. But, for dosing separate ferts in the aquarium you can dose them one right after another, and at worst the iron will end up on the substrate where it will only be available to the plants through the roots. If you dose the traces first, then wait a couple of hours and dose the macros, there should be no problem at all.