No sulfur problems, etc? Iron and hardness are readily dealt with. There are lots of water conditions that are not so easily dealt with. Think of the people with silica, arsenic, and other stuff that is harder to deal with.
If it was not clear, the people posting here would suggest a separate iron filter followed by an appropriately sized softener. The fact is that a softener will also remove iron, but besides needing more salt, it need to be regularly treated with Iron Out, or some other thing like Rescare. That backwashing iron filter will usually also deal with some other things too. My iron+sulfur filter uses Centaur Carbon. It was a big help. Katalox Light can deal with those and more.
Now is the KDF going to help? I don't know.
http://www.premierwatermn.com/kdf-water-filters-iron-chlorine/ says that KDF85 should have a backwash rate of 30 gpm/sq. ft. Softener resin needs about 6 gpm/sq. ft. Iron media usually needs backwashing more frequently than softener resin usually. There are controllers that do upflow brining. But usually those are downflow durning the service time. I wonder if they use some kind of controller to the KDF get hit by the water first.
There is a system that does not mix the media, even though they are in the same tank. MediaGuard would be like a tiny tank inside of the tank. That holds the KDF, and the water being processed hits that first. The water then continues on down. That appears to solve the major problems. The backwash will be stronger per square ft in that little tank, because the cross section of that is much smaller. Also, the KDF is there for iron removal. But dang, that is an awfully small dose of KDF. Is that sufficient? I don't know. But I feel it's got to be a lot better than just mixing the media.
The more conventional 2 tank system is going to take more space, yes. But it is less proprietary. And it is going to have a bigger dose of iron removal media that will be cheaper per cubic inch (I said cubic inch rather than cubic ft for lame humor effect.)
On a different point, 1 cubic ft of softener resin is unlikely to be big enough for 34 grains of hardness. Consider using the
http://qualitywaterassociates.com/softeners/sizingchart.htm and continue to the calculator link at the bottom. If you are cash limited, you could get a softener sized to handle hardness and iron for now, and then maybe put an iron plus whatever filter in front of that later (helped by the fact that you allocated space in advance). There have been a lot of intense discussions on that. The iron filter first is significantly better. The softener-only works pretty well, but takes some more maintenance.