Welcome to Michele's Forum -- and, Congratulations on your up-coming nuptials!     

Can't help much on the pilot questions, but I CAN opine that the lough Derg area is a terrific location with LOTS on offer.  It's a favorite for my wife and I.    http://www.discoverloughderg.ie/      

As to attire, what's appropriate depends more upon where you are from and what you are accustomed to.  My wife and I are long-time Florida residents, so we tend to wear warmer clothes on our visits to Ireland -- even during the summer months.  We've traveled with relatives who hail from Northern New York State, though and THEY were happy in shorts and short-sleeved shirts -- whilst we only occasionally were willing to forgo sweaters or fleece jackets.

Weather in Ireland is always unpredictable, but a good, rain-proof (and wind blocking) jacket is always a good choice.

See:   http://www.irelandyes.com/packing.html  for Michele's Packing advice.

Congratulations! May is my favorite month in Ireland so you chose a good time to visit. Even though you generally wear dresses, I suggest at least one pair of pants or jeans. However, denim can take longer to dry if you get it wet. Ireland is generally a casual place so unless you plan on doing something formal - go casual.

Thanks to Tony for those local links!