Signed up to the 220h. I live in Cork, 30 km from the start. So just thought I'd share some info.
Getting there:
Anyone flying might be interested in knowing that Cork airport is 6km from Cork city, but also on the road to Kinsale, where the start is. The airport is 20km from Kinsale, so consider going directly to Kinsale, which is a tourist town with lots of restaurants / shops. From Dublin, you could get the train to Cork and maybe cycle from there - while there are buses to Kinsale, it could be at the discretion of the driver to allow bikes. If you are cycling from Cork, get in touch and I'll send a quiet route (hint: the road from the airport to the city is one to avoid cycling on).
Elevation profile / Road Surface:
There were some questions on the elevation profile, I would say they are pretty accurate. The first 600km is brutal, as is the last 500km. The rest is just hard - rolling hills and not much flat roads for coasting. Expect many short but steep hills (12-20%). Adequate gearing + brakes needed!
The road surface will be a shock to many, we use "chip and seal" here. If you have done LEL, you might remember the Scottish roads - the roads here are worse. I will be running 35mm tyres. While its doable in 25mm (it is all on roads after all), I'd suggest min 28mm if possible
Irish motorists:
Irish motorists are generally worse than UK or Europe! You probably wont have any aggressive encounters, but some drivers here genuinely dont know how to interact with cyclists. Expect close passes and maybe stupid moves like overtaking followed by a left turn. One scenario to watch out for is the multiple overtake - first car does a good overtake, but then the rest all follow like sheep. The last car ends up skimming past on a blind corner. Also, since this is a tourist route, watch out for tourists who will suddenly brake and pull-in at random spots.
In case this puts anyone off, let me say that as long as you are vigilant, you'll be fine. I have never felt unsafe cycling in rural Ireland.
On weather:
Even though it is summer, the west coast of Ireland gets a lot of rain - twice the amount on the east coast of Ireland. There is a good chance that at least one day will be wet. Wind is generally from the SW, so mostly with us, except for for a few sections (750k / 1440k)
Hopefully that has not put anyone off! Its 100% worth it. The first few days are spectacular, particularly Slea head (loop after Dingle) if its a clear day.
If anyone has any questions, just ask.