If you stop on the glorious name: "Allah", how should the madd be treated? Is it al-madd al-'aarid lis-sukoon? Can you say "Allaaaaah" with 2/4/6 counts (depending on which is being used)?
Yes, the Glorious name of
has an alif after the
and before the ha'. This alif is not written in most of the copies of the Qur'an because it is so well known. Nonetheless, this creates a problem for those who are not native Arab speakers and are not aware of this fact.
When stopping on the Glorious name of
we have a medd letter (the alif) followed by one voweled letter. These are the conditions for
, so as indicated in the question, we stop on the Glorious name of
with two, four, or six vowel counts, consistent with what we are using for all the
in our reading.
Baarak Allahu feek, it seems like you have a good understanding of tajweed. May Allah increase you in beneficial knowledge.