Research and Rabbit Holes

I have been thinking about research lately.  So much so, I almost feel as though I should capitalize and underline the word, as in “I have been thinking about Research lately.”
 
You see, I am at the stage in revisions for my current romance manuscript where I am looking for places where I need to do more world building or add historical details.  Hence my dilemma.  How much world building should I do?  And how many historical details should I add?
 
I love reading a book by a good storyteller who can make me feel as though I am learning about a previous time and place while enjoying a great story.  One or two authors come to mind who deftly add interesting details I never knew – and never knew I wanted to know.
 
However.  There is a flip side.  If the addition of details is not done well by the author, it can become tedious, or almost come across as a lecture.  I do not want to be that writer!

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Perhaps you can see where I am going with this.  How many details should I add?  And what types of details should they be?  These questions tie back to my opening comment, since above all, I want to be accurate.   What is the right type or amount of research I should do to get the right type or amount of details?  It is all too easy to dive down a rabbit hole while researching something which, while interesting, is not germane to my story. 
 
Last night and this morning were a good example.  I wanted to know what breed of horse might be pulling a heavy wagon on an English road in my Georgian historical romance.  So while I was at the bookstore last night, I cruised the bargain aisles for books about horses.  I found two, so then had to decide which one to get.  This morning, I spent time paging through the chosen book looking for a likely horse breed – only to decide later that it wasn’t necessary to be that specific.  So while it gave me a chance to look at beautiful photos of horses, it wasn’t very productive in the end.
 
Perhaps I will toss the question out to you, my readers, for some input.  If you were reading a romance which took place in England in the mid-1700s, what historical background or details or descriptions would you like to see included?

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