1: I have never seen any mention of "Rep" or "Reputation".
There is "influence" which is used as a cost for certain units, and you can trade it to the AI, if you have much influence trading will go smoother in your favour.
There is also "Prestige" which boosts growth in each of your cities
Crystal, Metal, Horses, Wargs, Mana, Research, but no "Rep"
(To my knowledge anyhow, depending on whether you are playing a modded game and me being ignorant to 1 specific item used for next to nothing 
)
2: AI demanding tributes... Well yes and no, on average: Not really, I always reject any offers I get from the AI because the UI is terrible at telling me what deal I actually will end up with.
3: I never really look at strong/deadly etc. anymore, its based off some odd mechanic, it gives you an estimate based off HP, Damage, Defense, and special abilities, it should help you out when you don't know better, but its far from perfect.
Sincerely
~ Kongdej
