Greek numbers in Unicode

Question: which of the various Unicode codepoints for Greek numerals (in the U+03D8-U+03E1 range) should be used by preference?
Speaking descriptively not prescriptively:

(1) Re the upper- and lowercase forms for archaic numerals, although of course all characters on inscriptions (and presumably seals) are technically uppercase, editors may choose to render then in upper- or lowercase depending on editorial preference, and in some cases this difference is even meaningful (lowercase representing units, uppercase thousands, for example). Unicode merely reflects this practice. While I woulod strongly recommend anybody using these to be consistent within their project/corpus, I don't think it is possible to impose consistency across the field.

(2) Re the two koppas (Q-form and lightningbolt-form, for want of better terms), my understanding is that the Q-form is the archaic letter and the numeral 90 throughout antiquity. At some point (I think fairly recently) the lightningbolt-form replaced the numeral and is now so used in modern Greek chapter numbers and the like. I don't know if the two are ever used in the same text with different meanings, but Unicode has clearly decided to encode the two as separate codepoints. I would suggest that when encoding ancient Greek texts, we always use the Q-form, whatever the actual shape of the glyph on the stone/seal/page.

(3) I presume there's a similar situation involving the stigma and F-shaped digamma, when used as numerals; the latter is also sometimes an alphabetic character. The difference being that I believe most people having encoded numerical digamma=6 using the stigma codepoint.

Question: which of the various Unicode codepoints for Greek numerals should be supported by fonts/keyboards?
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Question: What variant forms of Greek numerals would be useful in, e.g. an OpenType font?
... (see also Greek Fonts (variant character forms))