Is this an offer?

I just got an email this morning from a job I interviewed for a couple weeks ago. This is my first choice and pays the most out of the ones I’ve been interviewing for. In the email, the guy said he hoped I had a happy thanksgiving, (I prepared myself for a rejection email), and then said to let him know “what my preferred timeline to start would be.” That’s it.

Is this an offer? Or is he just trying to get an idea of when I could start if I got an offer? I’m not sure how to respond to the email. Do I thank him for the potential offer? Or just give him my dates?

Also - I addressed my thank you email to him “Dear <last name>,” and he signed this “Thanks, <first name>” Should I respond Dear Firstname now or keep it formal?

Thanks!

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