I am a harper and have played for 16 years...
Most of what you say is true except
There is no existing harp attributed to O'Carolan- the harp in Trinity college is an example of a medieval harp, often called the "Brian Boru" harp (it didn't belong to him either) It was strung with wire, but the gut strung harp did in fact precede the wire harp, and was quite abit larger (drawing wire to the length required was difficult and so the wire harp was smaller) There are only a couple of contemporary paintings of Caroland and his harp, and unfortunately, artists tend to not be very accurate when it comes to harp depictions.
Regarding the music,
At the time of O'Carolan (the Baroque period) extemporaneous improvisation was the fashion, within the context of the piece. Naturally, Carolan was anxious to please his patrons who demanded that the music be up-to-date. If we remember that Handel premiered the Messiah in Dublin and that Geminiani is buried in Ireland, it is no wonder that Carolan's music has a Baroque flavor. (Some say he was the first Irish musician to go baroque- chortle)

The after dinner entertainment in an aristocratic house consisted of members of the household playing tunes together on violin, flute, cello, harp, harpsichord and sometimes guitar. A Scottish contemporary of Carolan was James Oswald and he wrote arrangements of what we now call session tunes for "Talented amateurs" that feature the figured bass, which means the chords had to include the bass note, but could vary. There are some great accounts of extended parties with various musicians sitting in,(and falling out) as well as musical arguments in pubs and the results of too much liquor on the music and musicians.

Incidentally, Carolan played left handed with his fingernails after the ancient tradition. The Welsh still play left-handed. Apparently it was thought that the left hand was feminine and so would have a high voice. You will see in all the old paintings that the harper plays the treble with the left hand and holds the harp on the left shoulder (very sinister). The change to the right hand came in the 19th century and nobody has given me a satisfactory reason why. I personally believe it has to do with the advent of the piano-forte where the treble is played with the right hand. It also may be a result of the harps being retrofit with levers to accomodate the "new" chromatic music

For those interested in harp lore, two great books are

Carolan- the life and times of an Irish Harper by Donal O'Sullivan
and
Tree of Strings by Alison Kinnaird and Keith Sanger

But don't "harp" on it!
*grin*

Julia Lane