Another Travel Question

Apologies for barraging my readership with travel questions of late, but I know a fair number of you have travelled internationally more than have I, so I figure this is a good forum for it. đŸ™‚

About how much cash should we have on hand before getting to Ireland? Should we convert any currency before arriving? Or just plan on withdrawing Euros from ATMs (which seems to be what most sites recommend) and/or exchanging cash while there?