How big is the cylinder tank? I have a Kohler faucet in my kitchen at this time. Can I divert to this faucet when needed for filtered water?

Needs to be a separate fixture.

The tank is about 12" High and about 10" wide. Diverting to the Kohler when you want it may be too complicated to acheive. Contact a plumber to see. Otherwise, I would either keep it on a separate faucet at the sink or route it to the refrigerator for the icemaker and drinking water spigot.

Yes. I have my complete system under my kitchen sink. I have the storage tank under 1 side and the filters mounted on the other side. The tank is about the size of 1 and half - 2 of the plastic gallon size milk jugs The only way to use it is this system is with the faucet that comes with it. Now you can buy another R.O. faucet that has more style. The faucet that comes with is fairly plain. If you get another designer R.O. faucet just make sure it is the vented type as the system is designed for a vented type faucet. I still have room under my kitchen sink for other stuff as well. It was easy to hook up and mount. I like the water more than bottled water. Unless your sink already has a hole for the R.O. faucet in it you will need to use a hole saw and cut the hole in the sink, next to the sink sprayer is where I put mine. Some sinks have a stainless plug on them for mounting say a sprayer or dishwasher vent. If you have a plug on your sink or even have a space where there used to be a sprayer or dishwasher vent you can mount the R.O. faucet right there.