I use a Mavea flowmeter to determine when to change my filters. I have a Everpure based system, the H1200. I had my residential water testers and this system handled most of the impurities that were are concern to me. Before purchasing a system, i would send a sample of the water in your home to a local lab. The local Water Authority should have a water analysis report on their website but I found quite a few variations in the results from my home and their report was about a year old when I reviewed it. I remember that is cost roughly $60. I still have a whole house water filter to attach to the incoming cold water to the house but that is phase three, there are always phases :-)
I agree with putting it in a convenient and accessible place. I am having my plumber move it to the utilities closet in September. The filters twist of easily but clearance in front and behind it would be nice. I replace the filters roughly every 8 months based on flow rate. My filter goes to a filtered water faucet and feeds the ice maker and hot water dispenser. I have a separate filter for the coffee maker.
Good luck!
Q