A good rule of thumb for us has been 10-20%, depending on the initiatives it can be more such as running the @lovesniper curation for instance is very time consuming and exhausting due to so many scam attempts and other activities the curators undergo such as leaving comments suggesting communities they may be interested in, following the genuine looking ones to curate them more later, etc.
Main point is to use common sense and fair rewards, comparing this to ocd for instance it would be as if we only used 10-20% of our voting power curating posts and then the rest trading votes with others who would vote our reports back, or even worse our personal accounts.