Filter useful life is rated in total gallons. You can figure out what you use. Some recommend a maximum time, often 6 months, regardless of usage. That is based on the possibility of things growing in the media!
Carbon is what takes out the chlorine. The low micron part of the filter is for other chemicals, organizms, etc. Lower micron is better in an absolute sense, but may or may not be something you need. Lower micron is same physical size will mean lower flow.
The spec data sheets on filters can be relied on for comparisons. Disregard the LARGE PRINT in the advertising hype!
I have never been a fan of whole house chlorine removal. You now have a hundreds of feet of pipe full of non-chlorinated water, and things happen.
I have noticed that the inside of the PE tubing on the outlet side of my undersink filter gets gunky looking after a while. I just replace the tub once a year.