I've been working on a book for the past three years now. It started off as a humorous account based off of real life experiences, but after many edits, it is now in the YA fiction genre. Also, I intend on this book being part of a series. What I'm wondering is if I should mention this information in my query letters. Is it even relevant?
Please do not mention the circuitous route your book took to reach its final (illustrious we hope) form. This is akin to watching food prepped for a beauty shot on a cooking show (blow torch, paint and glue, yum yum) or Miss America practicing her fire baton routine. It's better just to see the final result.
As to whether your book will be a series, my standard advice is to treat the novel as a stand alone at the query stage. You've got to get one published before you have two.