QUESTION: Here’s what I'm wondering as I'm setting up my “alternate earth.” If the reader’s suspension of disbelief is necessary to enjoy your writing, how do you know what kinds of things might be too much for your readers? Might pull them out of the story as they puzzle over why someplace that’s earth-yet-not-earth has *that*?
If your world has internal consistency and follows its own logic, most readers will accept that world. Readers want to believe your world. That's why they buy your story.
Things like dogs and cats and pine trees are just simple shorthand to make that world comfortable for the reader as well as making it easier for him to connect with it.
If the reader has to learn everything from the names of the trees to the five different kinds of six-legged beasts of burden, and they really have nothing important to do with the story, he will be seriously put off. Readers like comfortable, shorthand things like pine trees and horses.
Touches of the strange will liven up a scene to give it a sense of elsewhere, but there need only be touches. In a scene where the hero and his friends stop at a staging inn to rest their horses and get a meal, you can have the usual things like the tavern, the stablehand, and the horses, but you can also mention a corral filled with hippogriffs who are fluttering their wings and snapping their beaks as one of the servants tosses them dead rabbits.
But detail for the sake of detail will delay the action and cause the problem you mention. For example, the hero is walking through the woods, and a tree of living flame stops him in his tracks because of its beauty. It begins to sing of the glory of the wind and the majesty of the rain.
The hero finally moves away and promptly forgets it, and it has nothing else to do with the story.
The reader will wait the whole novel for that scene to make some sense with the plot, but it never does so the reader gets angry.
If, however, that singing tree gives the hero a riddle he must understand to achieve his victory, then the scene is very important, indeed.
Somewhere along the way, it would probably be best if the reader learns why the tree gave him that clue so the plot has some internal logic.
You also need to decide what your story is really about. If it’s about the unusual political situation in this world, then most of the extra details and information should help focus on that. If it’s about the world’s magic and how it is failing, then that’s where the details and the weirdness should be focused.
Most of this boils down to not overwhelming your reader and avoiding info dumping to show off your incredlbie worldbuilding skills.