Good news: none of the following elements belong in a query for a novel (and sometimes not even memoir).
You may be very concerned about demonstrating a certain value or judgment or lesson through the characters or story line. You might summarize this in a sentence or so near the end of the query, e.g., “Through Olivia’s journey, we learn what it means to love others, and through them, love ourselves.”
It’s not a problem if you mention such a thing briefly (usually after delivering the story premise), but if you have a full paragraph dedicated to explaining the novel’s overarching theme, it may make your work sound pedantic or too self-serious.
Don’t be tempted to elaborate on the audience or market for your novel. This is often misunderstood since nonfiction writers do have to talk about market concerns. However, when it comes to selling fiction, you don’t talk about the trends in the market, or about the target audience. You sell the story. I often encourage memoirists to follow the same principle and leave out readership information—save it for the book proposal if it’s requested.
Also, novelists don’t need to discuss their marketing plan or platform. Sometimes you might mention your website or blog, especially if you feel confident about its presentation. The truth is the agent/editor is going to Google you anyway, and find your website/blog whether you mention it or not (unless you’re writing under a different name).
While having an online presence helps show you’ll likely be a good marketer and promoter of your work—especially if you have a sizable readership already—it doesn’t say anything about your ability to write a great story. That said, if you have 100,000+ fans/readers on Wattpad or at your blog, that should be in your query letter.
First, make sure that you’re reading the guidelines closely. Nearly all agents want marketing and platform information for nonfiction authors, but not for novelists. Second, if the submission guidelines state they only want a query letter, it’s likely they seek clarity on your genre or category, plus basic information on your background and writing community activities. It’s rare for an agent to ask an unpublished novelist for a full and separate bio statement, marketing plan, or anything else that is more appropriate for a nonfiction book proposal. I would even go so far as to say that if an agent asks you to submit a bunch of marketing or platform information along with your novel query, you probably should look elsewhere for representation.
Sometimes authors hire a professional freelance editor to do a high-level edit, copyedit, or proofread on their manuscript; the motivations to do so are as varied as writers themselves. (I don’t think it’s necessary to do it before submitting, and in many cases it doesn’t increase your chances of a book deal—but that’s a different post.)
Regardless of one’s reason for hiring an editor, I don’t think it helps to say your manuscript has been professionally edited. This statement has become so common as to become meaningless—it doesn’t indicate the manuscript will necessarily be any better than one that hasn’t been professionally edited. Sometimes, in fact, it can indicate the manuscript isn’t very good. (Freelance editors can unfortunately do as much harm as good.)
If you have been working long term with a specific mentor who would be well known to the agent, that is fine to mention, but…
Similar to the “professional editing” qualification, novelists can be tempted to quote praise or positive reviews they’ve received from mentors, editors, critics, or published authors. It may make you feel good to have this feedback (and you should celebrate it if it was hard won), but this material isn’t helpful in your query unless the person is well known and trusted by the agent you’re querying. Even then, if they are well known by the agent, it begs the question: Why didn’t this person make an introduction to the agent on your behalf—that is, provide a referral of some kind?
In the end, the agent has to be enthusiastic and fall in love with your work—in addition to seeing a place in the market for it. They’re not going to rely on the opinion of a third party, and including praise from others can just as easily backfire rather than support your pitch.
Note that nonfiction authors (especially information-oriented books) are encouraged to solicit testimonials or endorsements for their work prior to publication, which should be included in the book proposal. One or two of these testimonials might belong in the query. But the same does not apply to novelists. In my 10+ years of editing queries, I have yet to see a testimonial for an unpublished novel or memoir that was worth including.