Okay...
Clouds, weather generally, unpredictable, no skirting around that. The one benefit is that the weather is also hugely changeable, whatever is going on, it won't last. If I had to pick a month to try Ireland it would be September. Typically they are pleasant, not that hot, but sunny with plenty of change. You may get clear mornings and dramatic evenings.
The car rental situation is same as everywhere, there's the usuals. Probably a bit cheaper than the US if anything. Do consider additional insurance to cover excess if you haven't already got a policy covering that. The narrow twisty roads, especially in the scenic areas will command your attention, and you'll be challenged compared to driving in the US. So if you're traveling with another, definitely try to have them drive, you can look out the window and spot what you like. You'll both need to present your drivers licenses at the rental counter.
Accommodation... there's Airbnb of course. And regular old Bed and Breakfasts. I'd mix them in, with hotels in larger towns.
You will find that in remote areas you will eat in pubs and hotels. Lots of great food in cafes and restaurants in towns but usually out in the country, food is in a pub. You'll find plenty with espresso too, don't worry. It's not all about the drink. Coffee culture if anything is better than the US. Pubs vary of course, but there's a lot of standard fare. I'd check out fish when you can, chowders etc, given the coastal aspect, but you can always look up farmers markets, great one in Galway town for example every Saturday, lots of vendors with food to eat or take away.
You could always check out Flickr and other sites for geotagged images, I tend to use Google Maps and Streetview to aid planning location visits, bearing in mind the extreme wide angle used, but definitely helps.
Dublin is cool and you will enjoy time there too, but if you're hitting the West you might consider flying into Shannon and rent from there, Clare the county is amazing and then onto Galway, you can travel along the coast towards Clifden, then north into Connemara to Leenane and then Mayo, the mountains there are wild and bleak. I'd check out Achill too. You could visit Clare Island and stay overnight.
Take your time, don't try to do too much. We are always amazed at visitors who dash everywhere, from Kerry (incredible admittedly but packed with tourists) and then all the way up to Donegal (also gorgeous and packed with crazy locals). It's understandable to want to see it all, but I'd suggest to slow down and see what you can take in with a slower pace. If Mayo is your target, it's a worthy one, drop into a spot or two in Clare and Galway on the way there and back, but settle and spend time in Mayo. Always found the people there very friendly.
