When it comes to Ireland there's a plethora of information out there.

There are a few different scholars with some excellent articles, such as Tomás Ó Cathasaigh and Liam Breatnach, although I recognise you're looking for books.

Roisin McLaughlin has published, Early Irish Satire which is an absolutely fantastic book. In the last couple years, Eoin Mac Cárthaigh published The Art of Bardic Poetry: A New Edition of Irish Grammatical Tracts I.

The largest current project concerning bardic poetry is the Bardic Poetry Database. There are three directors: Damian McManus, David Dickson and Ian Campbell Ross. The database itself also credits Katherine Simms. This is a database of the actual poems, and not an overview of traditions, so it may not be helpful for you in early stages.

Heya! You might be interested in our series on Finding & Understanding Sources, particularly How to Build a Secondary Bibliography and How to Tell If a Source Is Any Good. The posts in the thread talk about where and how to get started, how to identify the most important works of scholarship, and how to construct a general mental picture of the overall field.

Good luck!