Hi,I had "Be Thou my vision" at my wedding. A great hymn with a beautiful Irish tune. I think it sounds very Irish, (especially with verses about "High King of Heaven") My mum didn't want us to sing the one about "Be Thou my battle shield, sword for the fight," she didn't reckon it was appropriate for a wedding, however we sang it anyway.
"I heard the voice of Jesus say," is beautiful done to the tune of "Mary from Dungloe." (Let me know and I'll post the tune if you don't know it.)
I played for a lot of weddings, but one that sticks out was for a friend who wanted her favourite tunes played, so there was a guitar doing finger picking and me on flute playing all sorts of tunes in the background while they received the sacrament.
If you play them as instrumentals you can get away with a lot more, (anything can be slowed down, even Mairi's wedding!!...)One's which work really well include, She moved through the fair, Give me your hand (Tamhair dom do lamb), Carrickfergus, ....any slow Irish airs.
Let me know if you need any tunes.
Slainte
alison