Thank you @andypiper for your helpful answer! Finally I have an official answer 
However, one more important question:
Okay, I don’t need all this “overhead” of replies/retweets to that user for my use case which will likely make it impossible to use the streaming solution then (which would fit apart from that 1% threshold better). Did I understand it correctly that I am allowed to do REST API requests on behalf of the granted user tokens then as much as I want (like for example at a peak of total ~1000 req/min) from my server as long as I don’t make more than the 900 requests in a 15min time window for each of the users for statuses/user_timeline? Of course I would do each of these requests only if it’s really necessary (after sending very few lookup requests to know which requests need to be made).