I'm not an Irelander, but I'm an American who has been to Ireland 3 times and will be back a fourth in December. I'll try to answer your questions from a tourist's point of view.
1. Does it rain a lot in the month of April?? Yes, but it rains pretty much the whole year round. Typically July and August are the warmest and driest months.
2. Are the hotels and B&B usually booked up in April? I was in Belfast (Northern Ireland) on Easter 2005. I thought that it would be hard to find a place to stay during the holiday and was worried since I hadn't made any prior reservations. It actually was fairly easy. I've never made reservations ahead of time for any of my trips, and I've always found rooms. It's more expensive during the summer months though.
3. What are the coolest islands to see? I'll have to get back to you after December. I haven't been to any of the islands yet, but I'll be (weather permitting) going to the Aran Islands.
4. Where can we take a good seaweed bath? I would recommend Celtic Seaweed Baths in Strandhill, County Sligo. Here's their website for more info:
http://www.celticseaweedbaths.com/
5. What is the best restaurant to eat at in Dublin?
I mainly ate in pubs and small cafes to save money, so I'm probably not the person to answer this question. Here is a website with the top 10 best rated restaurants:
http://www.suite101.com/article.cfm/trav… (scroll to near bottom of page)
6. Do the Irish people like American tourists? They seemed to. Nearly everyone I met seemed really friendly and open. I think as long as you are polite and keep quiet about controversial subjects (politics, etc.) you will be fine.
7. What is the best tour to take while we are there? There are so many great ones! If you're in Waterford, don't miss the Waterford Crystal Factory's tour. Also, Dublin has great city bus tours that show you all around the city so you don't miss any of the great sites.
8. How long is the bus ride from Dublin to Killarney? According to the Bus Eireann website, it looks like it takes about 7 hours (with a stop in Limerick).
http://194.106.151.88/jplan/bin/query.ex…
9. Do I ask really stupid questions? No, actually they're good ones. :)
10. Where do the cutest irish men hang out, 40 and older? All the usual places, but normally wherever there's music and ale. I'd try the pubs or at the Guinness Factory.