Reddit mentions of An Introduction to Ancient Greek: A Literary Approach

Gunch is right, Koine is much easier, but it's also much less satisfying and less useful if you want to read anything besides the New Testament. There is actually a sub-reddit devoted to this, /r/IntroAncientGreek, that you might want to check out, and /r/AncientGreek will be a better place to crowd-source an answer for this. If you want hardcore grammar learning, I would suggest Hansen and Quinn but I also recommend Cecilia Luschnig's book Intro to Ancient Greek: A Literary Approach which will have you reading actual Ancient Greek texts MUCH sooner than Hansen and Quinn. It's a rather difficult language that will be difficult to learn without supervision and someone to answer your questions, so maybe get an answer key? Best of luck, and Χαῖρε!

Most people have responded to your desire to know more about how Greek evolved. However, if you want to learn Classical Ancient Greek, I strongly recommend Luschnig, Attic Greek. It's a great book. I learned Greek from it, and have taught Greek from it. https://smile.amazon.com/Introduction-Ancient-Greek-Literary-Approach/dp/0872208893/