For starters, surf the net and fill up with info concerning brackish and sea water treatment options. Here's another website full of descriptions and pictures:
Well Water Filtration Systems, Acid, Low pH, Iron, Bacteria, Manganese, Odors
Use the blue menu bar on top of the page to navigate and learn. I don't know if I would recommend buying from this site, as it contains some of the elements that the well guru guy advised as "shady sales tactics", but the site has lots of practical info. This site as well as many others have forms you can submit to request quotes on recommended systems as well as numbers to call to talk to an "expert" with no real commitment on your part.
The pretreat stage OffGrid described is known as air injection filtration. It oxidizes the soluble iron in the water without using any harsh chemicals. Once oxidized, the iron turns insoluble and can be filtered or settled out. You will definitely need an iron-removal stage in your system. And some sort of suspended solids filter after it.
Your water is well into the brackish range. The only real differences between brackish and sea water treatment are the concentration and the "trace" minerals. One favorable property of your well water is that it has such high salinity, the calcium and magnesium salts are less likely to foul your RO membrane.