We are running ours with just the spindown filter so there is no continued expense in operating it. I have a uv light but it is broke and i never repaired it. My main concern is that no sunlight hits the water. That's all i have. While the rainwater only goes through my hot water heater (cold water side is well water) , it is used for cooking, bathing, brushing teeth, dishes, etc. We have had no health issues.
There seems to be an upfront icky concern with rainwater here in the USA. If you go to other countries the ick concern is not there, primarily because it is normal to them. They use big tanks and allow sediment to fall to the bottom. They pull the water from the middle of the tank. As far as i can tell, uv filters are not used. But i say do whatever makes you feel secure about it. Peace of mind goes a long way.
Is the system automated? Are you looking for "city type" flow, or a basic off grid type system? A little more info on that will help. Mainly if it is a pressurized system. How to hold the pressure (pressure valve, back flow preventer, pressure tank). Thats where filter location comes into play. At least it did on my well side of system.