If you don't know how you'll eventually populate the device, impacting its power draw, I would lean toward supporting the maximum. That way you shouldn't come up short when there's a real event.
For UPS, however, it's a bit more complicated then the power draw on datasheets because with a UPS you need to figure how "long" you want to support a power draw. You'll want to multiply your power draw by how much time you want to provide it to select the UPS with the capacity needed.
