As with previous comments, this also reflects an experience from a few years ago. Hopefully it’s still relevant now. In mid-June 2011, we biked down the western-southwestern coast, from Galway to Dingle and beyond. For our first night, where our rental bikes were being delivered, we booked our B&B before leaving home. Same for a stay in Inishmor (a place that’s sadly no longer a B&B, and a cooking school/lodge in Miltown Malbay. Everything else, we mostly booked at a TI (tourist information office) one or two towns away, before we got to our stopping point for the night. One day, drenched from riding in downpouring rain, we pulled into a cafe to dry out, and gota recommendation for a B&B just down the street. They had room!
So 9 years later, with more access with smartphones and Internet listings, but also maybe more visitors throughout Ireland, maybe times have changed. Our last trip, driving and not pedaling, we wound up booking everything before we left the USA. We were in Clifden during a festival, wanted to guarantee a room at another small place way up north, wanted a specific base for hiking along the Antrim Coast (including the Giant’s Causeway), and had booked private guided historical tours out of Trim, so knowing where we wanted to stay and ensuring we would stay there, was important. But on the biking trip, the flexibility to ride more miles some days, and fewer miles other days, or stopping in a place that caught our fancy, it all worked. But we still seldom waited until we actually reached the town for the night, and phoned ahead that same day to book, or had a TI office up the road in another town help us locate a place (making more than 1 call a couple of times to find a suitable place), to eliminate searching once we got to our town at the end of the day. Not waiting until you reach that night’s town might be more helpful now, than it was back in 2011. And there were two of us, and as mentioned earlier, you’ll need to find lodging for three.