Hi. Welcome to ILF.
The y glide is always there, as is the w glide, but it stands out more in juxtaposition with an opposite vowel, i.e., a y glide (slender consonant) is clearest next to a broad vowel (a, o, u) and a w glide (broad consonant) is clearest next to a slender vowel (i, e).
Here I would say KAY is also fine for
cé without writing KYAY, i.e., KAY-vun /k´e:w´əN/ (where w´ is a v sound), but it is a matter of personal style/taste.
Slender
bh is a v sound, whereas broad
bh is a w sound, so there shouldn't be any need to put in an explicit y glide (but you might if you were from Munster, where the broad and slender bh are two different v sounds.)
As for the other questions, any long vowel tends to overshadow a glide vowel. In this case, you could just consider
-ibhi- to be a v sound. Irish has a spelling convention that dictates putting a slender vowel both before and after a consonant cluster where other languages would only put one after, and the same for broad vowel -
Caol le caol agus leathan le leathan.
A broad
c next to a slender vowel sounds like the que- in "question" or the qui- in "quiz".
A slender
c next to a broad vowel sounds like cu- in "cute".
Broad
n and
nn both tend to be pronounced /N/ in Connemara (and Ulster?) but may be /ŋ/ in Munster.
Slender
n is like the n in "any". No strong y sound.
Slender
nn is like the first n in "union", with a strong y sound, or at the end of a word like the gn in French
montagne (like a spanish ñ).
-io- is pronounced variably like oo in "book", like the oo in "kook", like i in "pit", and like yo- in "yon", depending on the word, even within the same dialect. Because there is no síneadh fada on either, dominance depends very much on the neighbouring consonants, e.g.,
iontach EEN-tukh /i:Ntəx/,
iondúil OON-dool /u:Ndu:l´/,
fionn FIN /fiN/,
sionnach SHON-ukh /s´uNəx/ or SHIN-ukh /s´iNəx/,
ionann UN-un /aNəN/ in Connemara.
If it were
-íonn then the
i would dominate and the pronunciation could be represented by either EEN /i:N/ or EE-un /i:əN/, depending on whether you recognise the glide as being a natural part of the N sound or feel a need to explicitly represent it (though I don't think it is really two separate syllables, more like one and a half).
It is also important to be aware that the ay in "day" in English is actually a diphthong /ei/ but the Irish language
é is a pure long vowel /e:/ (this is complicated somewhat by the fact that Hiberno-English uses a pure long vowel for ay in "day", i.e., /de:/, so be sure to say "day" with an Irish accent.

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(Crossed with Lughaidh, but I'm saying the same thing only in more detail.

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