Just want to say...I don't put a Keeper hut outside every habitat. I don't understand why people recommend that. I have one (small) hut for every 3 to 5 habitats and it works just fine, without queuing. I also assign my keeper work zones 3 to 5 habitats in a work zone, with 2 to 4 keepers in the work zone. That also works just fine. Doing 1 hut to 1 habitat with 1 keeper is overkill and unnecessary. You just have to make sure you have the keeper hut positioned nice and centrally and not too much distance to any of the habitats or the keepers spend too much of their time just walking back and forth.
The only exception is in an area where I'm going to build many smaller habitats at which point I may build a large keeper hut and have it covering 10+ habitats.
Currently I'm just running a small zoo for zebra breeding for the challenge, waiting until the next update to do more in a real zoo, but the principle is still the same. I have 4 zebra habitats, each with anywhere from 3 to 8 zebras in it and also an exhibit house with 6 exhibits. One small keeper hut and 4 keepers are servicing all 4 habitats plus the 6 exhibits and I have yet to have a queue once in the keeper hut.
Below is an image showing the positioning of the keeper hut (green circle) and the 4 habitat gates (1-4) as well as the exhibit house just off screen (5-11). Keeper hut building has been left with room to change it to a large keeper hut should I ever decide to add further habitats to the North, or even sides (opening space for a path between 1,2 and 3, 4 to go to the sides. Obvoiusly it's not pretty, it's just for breeding. But even when I go for aesthetics, I use a similiar approach, clustering 3-4 habitats at least semi-close together so one hut and the same keepers can service them.
Edit: should mention I also don't train my keepers past 2 stars unless they are serving a huge multi-species habitat with a ton of animals in it, or a lot of exhibits. You can hire 3 keepers for what a single 5-star keeper costs, so it's just not worth training them unless they have a job that requires speed.