for the most part the 2750 is not more durable than the 7000. They are both high flow control valves, the modern plastic valves are just as durable as the brass. The only item of concern with durability on any Fleck or clack system is to allow for some movement in the plumbing so that the tanks expanding and contracting under different pressures will not cause a tank failure over time.
I would recommend a Lakos twist to clean filter ahead of the equipment just to minimize the load on the turbidex sediment filter. You dont want to let heavier particles get into the turbidex otherwise it will become part of the filter bed
Chemsorb, turbidex, microz etc are all very simlar medias.
2.5 cu ft is fine, definetly get the 7000 for softening, the built on bypass is much more convenient than the 2750 which has no bypass
the standard resin is fine, Ohio pure uses a good resin for its base system.
The Turbulator is not needed. Be sure to confirm that the unit they are shipping uses the 32mm distribution system.