As someone who is interested in learning it all (Attic, Koine, Homeric, Church Fathers, LXX, etc.), I'm curious whether I should be wary of vocabulary and grammatical interference when reading different dialects. I started with Attic last December, and worked through most of Hansen and Quinn, while reading the JACT Reading Greek book and various other Attic readers (Moss' First Greek Reader, Rouse's Greek Boy, etc), but I recently completed a class in spoken Koine, and am trying to read through the NT, together with large chucks of the LXX and Church Fathers.
Beyond knowing that I won't be seeing a lot of dual, optative, or other Attic features, do I need to worry about reading a lot of Koine and then having trouble reading Attic (and eventually Homeric) Greek later down the line? Or is any Greek reading good for all the other dialects? As things stand now, I really see little difference between Attic and Koine, beyond vocabulary and simpler grammar for the latter dialect, but perhaps that's indicative of my level of Greek..