maximo wrote: For Instance, in
dual should I use tó and toîn with female nouns or tá and taîn?
I think the separate feminine forms were invented by grammarians. The dual is very rare in all but Homer and Hesiod, so I wouldn't worry much about that.
Is there a order to learn greek?
What greek dialect we learn in a common grammar?
Most people start with Attic, the dialect in and around Athens. All Greek grammars I know of in English assume this dialect, and then have separate sections or footnotes for other dialects.
As for how many dialects, there were quite a lot of them. However, our only evidence for most of them is local monuments. Most of us want to know the literary dialects, and that number is much smaller: Epic (which is Old Ionic with some extra stuff from other dialects), New Ionic (Herodotus mostly) and Attic. These are the big three, and have a great deal in common. Koine, the language of Alexander's empire and the NT is basically simplified Attic with some New Ionic forms and foreign vocabulary (Aramaic, Latin, etc.)
If you wish to read the poets Sappho, Alcaeus or some of Theocritus, you will need to know Lesbian Aeolic. This dialect stands most apart from the other dialects: different vocabulary, surprising sound changes and the accent rules are different.
If you wish to read Pindar, Bacchylides, Simonides and parts of Attic drama, you'll need to learn to recognize a literary Doric dialect. That has some vocabulary changes, and few simple sound changes (long alpha where Epic and Attic will have eta). This literary Doric is pretty simple. Real Doric, not well attested, is harder.
