Aristotle takes telos to be one of the four causes, yes, and Aquinas agrees with him here. However, telos is a more general concept than what you might call conscious human purpose. The cause-effect relationship is itself teleological. You could not explain why an effect results from a cause without telos. This isn't axiomatic, though, which makes it sound like it is assumed without reason.
And yes, you can indeed argue for the existence of God from telos, but this isn't question begging. The teleological argument Aquinas is famous for (his Fifth Way) is not the Paley-style argument some people think it is. Feser's article "Between Aristotle and William Paley: Aquinas’s Fifth Way" discusses this at some length, beyond what his book "Aquinas" discusses (you can find it in this book [2] along with other material worth reading).
> This said, are any of those books a good read for someone who doesn't think there's any purpose, reason or goal to all of this?
I understand that you lean this way, but perhaps a better stance is to be fair and open minded toward the subject. Apart from the books I already listed (which are indeed good), I might even suggest beginning with this popular polemical tract [0] (polemical because it responds to the snark and ignorant condescension of people like Dawkins), and later, if you are interested in an introduction that focuses specifically on the existence of God from five different philosophical positions, you might find [1] interesting.
And yes, you can indeed argue for the existence of God from telos, but this isn't question begging. The teleological argument Aquinas is famous for (his Fifth Way) is not the Paley-style argument some people think it is. Feser's article "Between Aristotle and William Paley: Aquinas’s Fifth Way" discusses this at some length, beyond what his book "Aquinas" discusses (you can find it in this book [2] along with other material worth reading).
> This said, are any of those books a good read for someone who doesn't think there's any purpose, reason or goal to all of this?
I understand that you lean this way, but perhaps a better stance is to be fair and open minded toward the subject. Apart from the books I already listed (which are indeed good), I might even suggest beginning with this popular polemical tract [0] (polemical because it responds to the snark and ignorant condescension of people like Dawkins), and later, if you are interested in an introduction that focuses specifically on the existence of God from five different philosophical positions, you might find [1] interesting.
[0] https://a.co/d/7tSlbxk
[1] https://a.co/d/arJWT56
[2] https://a.co/d/jaG30ac