Is there such a thing as too much research for a story?
It’s too much research when you feel that you must know absolutely everything about every aspect of your story, and because of that, you never actually work on writing the story.
It’s too much research when you feel you can’t write a scene because you don’t know enough about some of the details in it. Write the scene and fix the details later.
It’s too much research when you feel obliged to put all of the stuff you learned into the story itself because you worked hard on that, damn it, and somebody should notice.
In short, it’s too much research when it screws up writing the story.
How do you avoid too much research?
Get a general knowledge of whatever it is you’re researching. GENERAL knowledge, not in depth, enough to get started writing.
Encounter a place you need to know something. Make a note and keep writing.
When you’re done writing for the day, look up whatever it was that you needed to know. Make a note and fix it when you sit down to write the next day.
If you love what you’re researching, consider non-fiction. The truth is, 99% of what you know about your subject is not only unnecessary to your story, putting it in there will hurt the story. So unless you really want to be an expert on rat-catching in the eighteenth century, get a general knowledge of how rat-catching works and then go write your book.