While I'm not a huge Kinetico fan, I would also wouldn't generally recommend staying away from them. HOWEVER, in this instance, I would avoid your particular Kinetico dealer as he quite simply does not know what he is talking about. He may have a fine product, but he cannot be trusted to set it up correctly or to assist you if you have any problems down the road.
Yes, you absolutely have to bypass the exterior faucets if you use sodium choloride for regeneration and intend to water plants from those faucets. The sodium will kill your plants, both interior and exterior. Even with potassium chloride regeneration, it is recommended that you periodically water with other water, so bypassing exterior
faucets is a good idea regardless. RO water is fine for interior plants - just be sure to fertilize regularly.
If you go with Ecowater, avoid any softener that includes carbon in with the resin. I don't see a 2500 on their website, but do see a 2502 that looks fine. The 3500 appears to have carbon included. There are many reasons why carbon should not be mixed in with softening resin: 1) Carbon depletes faster than resin ages. Good softening resin should last 15 - 20 years. Carbon will not. If you are actually relying on the carbon in the softener to remove chlorine, you will, after 1 - 5 years, have to have the carbon and resin replaced (carbon is cheap, resin is expensive) or install a separate carbon filter. Good $$$ for the vendors, bad for your wallet. 2) GAC (granular activated carbon) is abrasive and will damage your resin, reducing resin life. 3) If the GAC mixes with the resin rather than staying in a layer on top (and it will mix - their specific gravity is pretty close), it is no longer protecting your resin from chlorine attack.
If you decide you don't want the extra expense of an RO, and honestly they are rarely necessary for city water, you could also have a small bypass line installed to an extra faucet for drinking water and plant watering. It depends on what you prefer, taste-wise. Some don't like the taste of hard water/some don't like the tastelessness of RO water.
Q
Addresses the specific concerns presented.
Q