iCloud Photo Library and storage usage on devices I am considering to use one of Apples iCloud plans.
I read that photos and videos on the devices are "lightweight versions" using less storage (at least if you configure it that way).

But let's say I have 200 GB of cloud storage filled with 190 GB of pictures, how can my iPhone with 16 GB handle that? (Assuming 16GB are not enough for the "lightweight versions" of the photos)
Am I getting device storage warnings and alike?

Thanks.
It is not a lightweight version it's more like a preview and then when you're connected to the internet you have access to the photo in full resolution. Your iPhone will let some space to the photos it will just optimise the storage, not all photos will be in the cloud. But I'm not sure if it can handle 200Gb but some space in your iPhone will be used depending on how frequently you access your photos in the cloud.