As a newcomer to this site I'm trying to understand how it works. I answered the question Who was the first retailer in Monterey, California? and whilst I wouldn't expect my original answer to get many upvotes as it didn't answer the question I believe the additional information I provided in a modification was pretty comprehensive, properly sourced, and based on original research including this particular item Vallejo document which I would challenge anyone to find as there are 78 volumes of Vallejo documents, each containing several hundred pages, with no index. I also answered the question and again would challenge anyone to suggest that my answer is in any way incorrect. The previous answer to the question received 3 upvotes to my 2 and yet it didn't provide the correct answer to the question. So why hasn't my answer received more upvotes? What's wrong with it?
The number of votes received is very seldom related to the quality of the answer, but more so to the popularity of the questions subject. The question you answered is several years old, and has an existing, accepted answer, and as Mark points out is too specific to be of general interest for many of our users. Adding the length of your answer to the lack of general interest in such a specific topic, and votes may suffer accordingly.
(I don't think any one of us has not had the situation where we put a lot of effort into what we felt was a 'great answer', only to get little acknowledgement in the form of votes)
On answer length, the only advice I would give is make the answer as long as necessary, but no longer. If your answer is long, make sure we can find your conclusions clearly stated (perhaps summarized) so we can decide if we wish to read the entire body of the answer. (The TLDR is a thing here.) Personally on long answers with large quote blocks I like to see a little emphasis placed using bold to draw my attention to the relevant bits.
If you intend on participating further, I think you will receive a positive response from the community.