You probably need to get the K2006 and the better cartridges SO you can make it work.

I've operated numerous pools that were filled with iron contaminated water. Working out a process that is functional for THAT particular pool always took time. Usually, it wasn't till the 3rd season that I could run them without hiccups.

Operating a small pool, with undersized filters, that is filled with iron contaminated water is a task with a STEEP learning curve. If you aren't able to be patient and accept that there will be failures this year, as you work it out -- save yourself the pain and money, and bail out now.

But, if you're going to try to do it, do NOT put off what you need now, to make it easier. Of all the periods when you will want "easier", this is it. Later on, when you HAVE a method for your pool, you'll be able to 'get by' without this or that.