You will find a mix of opinions about that. Pre-mixing is easy, and doesn't result in granules of chems floating around the tank. However, there is no evidence to suggest that dumping a 1/4 or 1/16 tsp of granules of ferts into the tank is actually bad.
Basically, do it however it best works for you. You'll end up using about 4x the amount of KNO3, if used according to standard EI dosing, as all of each of the other ferts. And KSO4 may or may not be necessary, depending on your tap water parameters (K is supplied by KNO3 and KH2PO4). So, KNO3, KH2PO4, and micros (Miller Microplex or CSM+B) may be sufficient.
There's also an argument surrounding "red". Plenty of people will tell you that extra iron equals extra red. Plenty of others will tell you that the red has nothing to do with iron, despite common myth. As for me, I'm of the opinion that high light equals red, so long as there's plenty of ferts of all shapes and sizes.
KSO4 and Iron won't hurt anything, but they may not be at all necessary.