Sorry that I don't post about much else right at this moment, it's just that this has captivated my attention.
I've got the list of words that make up 80% frequency of appearance in Greek literature, I think it's a 1000 or so, plus a frequency list of NT vocab. My aim is that over the course of the reader all the 80% should be covered, and probably I will aim for every NT word above 30x. That is quite a lot of vocab, in some ways, but I will just make the reader as long as necessary.
I plan to rewrite the first chapter to make it not-a-translation from Ørberg, though I think I will retain the geography/map scheme. It really is a great way to get into the language.
My story is going to be set in Rome, AD, rather than 4/5th century Athens or wherever, for several reasons: because it allows Koine, over pure Attic. It allows a retrospective look at more Greek literature. It also allows a picture of Hellenistic world under Rome. Finally, it allows a Greek/Roman/Jewish interplay, and the introduction of Christian material. No doubt some feel that the inclusion of any 'religious' material will make the text unsuitable for politically correct secular institutions, but in my mind that is both a misunderstanding of secular space as well as historically naive.
I have no timeline, I just plan to write a little each day or so. I will probably try and draw up a schedule of what grammar to introduce when.