With or without iron filter? Actually, I am not sure how that would change my thinking, but it should. Also, are you referring to two 2.5 cuft tanks or two 1.25 cuft tanks? Flow rate (SFR) plays a factor. If it has sufficient flow rate for you, the two 1.25 cuft tanks sounds nicer with iron, but I am not sure at all. In reality, the tanks would each regenerate a little less often than a single 2.5 cuft tank would, but maybe the period of time after regen but before use should not be considered toward keeping a maximum regen interval if treating iron. Clearly the dual tanks are nice if your household does not have a regular schedule.
For the iron +sulfur+more filtering,
http://www.purewaterproducts.com/img/docs/manuals/Katalox-Light.pdf shows sizing is mostly determined by flow rate giving sufficient contact time, especially at your iron levels. I don't know of pre-configured systems that come with my controller of choice. Katalox Light is top iron+sulfur filtering media, and it is made in Germany.
Regarding resin, as far as I can tell from reading, Aldex, made in Canada, is also good resin. I don't know where most Purolite resin is made, but I expect they have good quality control. Their home page says they started as a resin importer.
http://www.softenerparts.com/Resin_Carbon_other_Media_s/24.htm says the Purolite C-100-E is made in USA. I don't know where their premium SST-60, which is claimed to be better if processing iron, is made.
I am not a pro, and I am curious about this too.