Q: What is the limit of data that can be compressed so i can move my photos and movies to the Cloud ?

It's as much an art as science so it's impossible to give a precise answer. Only you can make the decision as to what's the limit.

Do some tests. Keep on lowering the data rate until the quality doesn't measure up to your expectations.

Russ

Most format of photos are already compressed so compressing them again will generally gain nothing at all.