Do you have a water storage tank or is your water straight from the main, you need a reasonable pressure for backwash. We back wash ours monthly
One tank will do, you could put multiple layers of filter media in the one big tank or just the one media type, I like anthracite as a first line of defense, it will reduce the amount of silt and other <deleted> that comes through, then the Zeolite (the brand name I bought was Zelbrite) I got this from a pool shop, this will filter down to below 5 micron, then activated carbon.
Here's a pic I nicked from the internet to give you an idea.