Which websites satisfy my zoological enquiries?

At the moment I am mainly interested in learning as much as possible about ideal/possible/practical/productive animal companionship combinations.
For instance, would it be at all positive to let my pet rat and one of my rabbits get acquainted?
I’ve experimented quite a few already: Ducks/Hens, Ducks/Rabbits (quite pleasant when they become friends and eat together, but not very sanitary); Dog/Cats; Cats/Dog/Rabbits, Rabbits/Goats (also nice to see when bonding, but initially stressful to both AND not sanitary if kept together in one stable).
One thing I’m trying to achieve is to optimise their good moods and productivity, stimulate their curiosity/interests and social skills, and so on.
Their productivity notably varies from combination to combination, therefore I wish to eventually have them settle with their ideal mates.
Now, who to put with my young, lonely rat, without any sort of trauma?
Of course, as first answer I already know it all depends on the approach, etc. ..
Cheers!