Early May is not the busiest time of the year, but it is busy. Kinsale in particular is busy most of the year. I'd book ahead for Kinsale. A general "rule" of thumb is to book your first few nights and last few nights. In between these times you can "wing it"
With regards "winging it", be prepared to have to spend some time finding a place that suits you and your budget, and be prepared to sometimes having to take whatever is available. If you are not fussy this will not be an issue.
Accommodation providers prefer guests who stay for more than one night (at least two) because their profit is made on night two, so keep that in mind when booking in. It might mean the difference between getting a bed or not ! In any case you should try and stay at each basecamp for at least 2 nights and day trip from there.