I would not get too fixated on the 7-8 days between regenerations. Once every 3-7 days is average. The capacity of the system (30k, 45k 60k), the water chemistry and household usage determine when the system has to regenerate. The less a system regenerates, the less salt and water used, simple as that. That is the most efficient way to set it up. The capacity also helps determine the gpm flow rate through the system. In general 30k=10gpm, 45k=12gpm, 60k=15gpm. Matching the valve size to the plumbing size is a good idea, but will not solve the flow rate issues alone, as stated above. Fixture counts also need to be taken into consideration, toilets, faucets, dishwasher, showers.
Here is an example of sizing, regen cycles and flow rates using a capacity of 45k.
20 gpg x 300 gallons (4 people) = 6000 grains per day usage
45k - 20% reserve = 36k practical capacity / 6000 = 6 days between regenerations.
12 gpm flow rate.
Clack valves are quickly becoming the standard for the industry. They have very good electronics and are user friendly to work on. Many plumbing supply houses are carrying Clack valves now. A Fleck 7000 is a good choice in 1" valves and is available from ohiopurewater and uswatersystems.
As far as SST resin, it can be more efficient but I don't see that big of an advantage with it.
I would go the DIY route before I bought a Culligan. Way overpriced and they change models so frequently that parts are now becoming obsolete much sooner.