Lets start with the basics, thought this could turn into a huge debate that I am not interested in. Your local water treatment guy should know what to do regionally, but as soon as somebody recommends a softener for 5 PPM iron, I cringe.
Iron removal can be done with Pyrolox. This media is difficult to use, is the dirtiest media ever mined, and takes considerable backwash water but it eliminates the need for pot perm. If it is used correctly, it is one of the best medias ever. Used incorrectly, it is a nightmare.
You mention that you have tannins and that will likely be the cause of your fishy smell.
High hardness should be dealt with especially if you want to get rid of the tannins.
Here is my recommendation, this is a very unique system designed specifically for your application.
Stage 1: Minimum, A 9x48 Iron and hydrogen removal system utilizing Pyrolox. Please note that your pump needs to be able to pump 11 GPM to properly backwash the Pyrolox.
Stage 2, an parallel tank system with softening resin in tank 1, and Tannin selective resin in tank 2. This unique design eliminates the need for seperate regeneration cycles for the softener and tannin systems. The softener regenerant wast (chloride) is used to regenerate the tannin resin.
This design requires the addition of a resup feeder to lower the pH of the brine water so as to prevent the precipitation of the caco3 in the anion resin bed.
This would be the way I would do it.