The most advisable thing for you to do is learn what you want to read first. Learning Greek is not easy, yet it is not terribly hard either, especially if you already know Latin.
Iliad or Odyssey - Homeric Greek
Plato, Aristophanes, Sophocles, etc... - Attic
Lesbo - Ionian
New Testament - Koine
I'd start with Attic first, as it has the most works written in it, then move on to the different dialects (really easy to pick up, with the possible exception of Homer, you might need a brief tutorial) then move in late Greek (Septuagint - just got it today!) then Koine. But that's me.