thanks a lot for number two in this series! There are only a few minor things to add:
> Téora búada in catha-sin .i. maidm for Congal Cláen ina ainfír re
> Domnall ina fírinne, + Suibne Geilt do dul ar geltacht, + a inchind
> dermait do búain a cind Chind Fáelad.
> I have several questions about 'téora búada'. It seems to be a
> feminine genitive form, while 'búaid' is neuter and it's descendant
> 'bua' is masculine.
Yes, "búaid" is usually neuter in OIr. In MidIr., the neuter gender was lost, and former neuter words were too the greatest part assigned to the masculine gender in ModIr.,
a few went over to feminine gender. It seems that "búaid" was one of those words, that were assigned different gender in different dialects (?). Ó Dónaill's Irish dictionary
says that "bua" is masculine, but in Dinneen both genders are given, and in Scot. Gaelic (source: Colin Mark's new dictionary) "buaidh" is feminine. So the feminine
gender, expressed by the feminine numeral "téora", needn't puzzle us overduly.
Since we are not idealising the text, we can leave "téora búada" as it stands. If we were to create a normalised OIr. text like in EN, we would emend it to "tri búadae".
You translate "búada" as "benefits", which is not unfitting. But especially in triadic expressions like the one we are looking at the more usual translation would be "special
quality; remarkable quality; attribute, virtue".
> Also, why is it genitive at all, is it some kind of predicative?
No, "téora búada" is just the plain nom. pl. In earliest OIr., the feminine nominative of "three" was "téoir, teuir...", but already in the glosses the form "téora" is attested,
which was originally the accusative (see DIL T 303.59).
Note that what follows "téora búada" is a masculine genitive singular. Therefore the word after the article has to be lenited: "in chatha-sin".
> 'maidm for.....re' is a common formula in the annals. Along with
> 'maidm', the preposition 'for' designates the loser of a battle, while
> the preposition 're' denotes the winner.
Yes, that's a very common expression. The corresponding verbal expression is "maidid (cath) ré X for Y", where "maidid" is an impersonal verb. Sometimes the two
prepositional phrases are simply added to "cath", e.g.
AU 848.5 Bellum re n-Olcobur, ri Muman, + re Lorggan m. Cellaig co Laighniu for gennti...
"a battle (Latin bellum substituted for Irish cath) won by Olchobur king of Mumu and by Lorgan mac Cellaig together with the Laigin over the heathens..."
The vowel of "ré" is basically long, which can be seen from the fact that it can also appear as diphthongic "ría" (as in E2). "ré, ría" nasalises, therefore "ría nDomnall".
"ina anfír" and "ina fírinne" are both prepositional phrases consisting of "i" "in" + 3rd sg masc. possessive pronoun, i.e. "in his untruth" and "in his truthfulness". We would
therefore want to indicate lenition on "f*írinne". The "f" in "anf*ír" is apparently also lenited (see DIL A 147.5), although the spelling "ainbhfíor" which indicates a nasalised
pronunciation of "f" is attested in Keating.
Note that our guiding MS E2 and A do not have "anfír", but the synonym "gae", MidIr. dat./acc. of "gáu, gó" "falsehood". In OIr. this wouold be "goí". I would keep it here,
first because it is supported by two out of 3 MSS, second because of the lexical variation.
> It seems to me that 'geilt' signifies the state of madness, while
> 'geltacht' is the terror or panic that causes insanity.
No, "geilt" is simply the adjective "crazy, lunatic etc.", whereas "geltacht" is its abstract "craziness, lunacy".
You chose the preposition "ar" after the verbal noun "dul" "going", taken from E1. E2 has "re", which is probably MidIr. for "fri". I don't think we can easily decide which of
the two prepositions is better; I would simply keep the reading of E2, but maybe adapt it for clearness' sake to a more classical spelling "fri".
"dul fri/ar geltacht" is not so much "transported by terror", but rather "going into lunacy, turning mad".
You were correct in chosing "búain" as verbal noun in the last part of the sentence.
My suggestion for normalisation:
Téora búada in chatha-sin .i. maidm for Congal Cláen ina goí ría nDomnall ina f*írinne, + Suibne Geilt do dul fri geltacht, + a inchind dermait do búain a cind Chind Fáelad.
Other comments, suggestions, additions?