Late the party but...
Don't do a pelican system. Nobody I know that has them (or similar systems) are really happy with them vs. a traditional water softener.
If you want it anyway and understand how your water will turn out, fine. But you will not get the water quality of a traditional water softener.
Ideally I'd think 10"x54" tank, 1.5 cu. ft. systems should be fine, and I'd prefer each tank (carbon/water softener resin) have individual control valves. Several systems exist to do carbon/softener with one valve, but if you can do it with individual valves, you're better off as the carbon should really be changed out every 3-5 years on municipal water.
Don't venture outside of Clack/Fleck/Autotrol on control valves (Fleck is your most likely to find online, Clack only sells water dealers, but are what I personally prefer if price was close to equal).