The query letter is separate from the pages, synopsis, and anything else you paste in the body of the email. It’s a business letter, and your signature needs to be at the bottom of it.
Signatures should not be floating at the very bottom of the email after everything else.
The display name for your email address doesn’t have to be your name, but it looks better. “Janet Shepard” is more professional than “turtle lover.” I’m also astounded by the number of women who use their husband’s email to query.
A weird display name doesn’t earn a rejection, but it says you don’t know to conduct yourself in a businesslike manner. You can change the display name in your email settings.
Many industries no longer require letterhead in official emails. You’re still welcome to put your name, email, address, and phone number at the top of the email. It gives a nice, clean look. Just know it’s not a must in order to appear professional.