You absolutely need carbon filters for SF water, we do have chloramines, and you need to filter those out before your membrane. "SF water is pretty clean" is a TDS thing, which unless it's super high isn't really a sign of cleanliness, it's just a relatively easy measurable we can look at.
There aren't really any gauges to tell you when it's time to change filters either, TDS meter sure, but that is only for your RO membrane or your DI resin. You can buy a flow meter to record how many gallons go through your filters, but that's not really a sign of if they need to be charged because depending upon how aggressively water is "cleaned" they may go sooner rather than later. Sediment filters can be visually inspected for replacement, but carbon filters the best you can do is put in a TEE between filters with a valve to take water samples and then use something like a chlorine test strip. Or the best solution is to not try and squeeze every last useful molecule of carbon from your prefilters just swap them on a 6 month* basis and call it a day. *or whatever time period due to your total water usage if you use it for a 300 gallon system you'll burn through filters much quicker than if you use it for a 30 gallon system most likely.
That said if you want to ditch the RO filter idea and have zero waste, you can simply use tap water plus prime, and maybe set up some sediment filters with a pump loop to clean out any larger garbage in the water column.