Wow, detailed question. I will answer it in a simple manner.
Membrane, it will foul over time thus reducing its flow rate, but possibly increasing its rejection of dissolved solids. Over time, it is not unusual to see a membrane produce less, but higher quality water.
It can also do the opposite. Over time, it can get microtears, or oxidation damage that slowly degrades the filtration surface that will allow more production, and lower quality water.
All that being said, many years ago a residential membrane cost 5-10x as much as they do now. Considering the low cost, it is now considered a consumable filter, not some fragile, high priced filter that we should spend too much time worrying about.
it was common practice to soften water ahead of small commecial membranes. now many companies simply consider the cost of salt compared to the cost of simply replacing the membrane more often, the salt is usually nuch more expensive than the membrane.
It is much more complex than this, it would take dozens of pages, but since the cost of the membranes is so low and theior durability is so much higher than it has been in the past, the need for training people how to protect their residential or light commercial membranes has been virtually eliminated. Simply replace the membrane when the performance drops out of specification.
Change all of the filters annually. For a well, a 3 or 4 stage RO should be fine. A simple 5 micron sediment filter, membrane, and a post carbon should suffice.
What is your water like coming out of your water treatment system? Do you have a water analysis you can post?