The water hammer problem can be soved with a pump control valve system at the pumping station. Use an air over oil check valve to slowly bring the flow through the force main up on pump start and similarly bring it slowly down before pump stop. The only electronic components are a simple PLC...
Sounds like you are on the right course to me. Regarding the temperature input, remember it is for BOD5 reduction which decreases with decreasing temperature, so winter removal efficency controls the effluent quality.
I would be comfortable using literature values for the hauled waste only...
Schrieber Corporation of Alabama makes screw pumps. See www.schrieberwater.com.
Don't know for sure about the medium bubble diffusers. EDI of Columbia, MO makes an excellent fine bubble diffuser. Might try Enviroquip too.
How old is the home and do you know what material the pipe is? If the house is less than 25 years old, it is likely PVC pipe. If properly bedded in gravel and two feet deep, it would withstand a car driving over it. I would not chance it with a RV. You could put in a section of ductile iron...
