PALMER family - Fermoy, Co. Cork

[Emms]

I'm a relative newcomer to genealogy, and I've run into a brick wall with my research, so I'd be grateful for some pointers if possible.

I have discovered that my gt gt gt grandfather William Gray PALMER married an Irish woman named Kate (surname possibly O'BRIEN or NEEDHAM) from Longford, probably in the late 1830s. Their first born son James was also born in Longford in 1840, but they clearly then moved to Fermoy where their next four children were born between 1842 and 1848. They had one further daughter in Limerick, and then crossed to England, probably around 1850.

Unfortunately I have no idea where to go from here! Can anyone recommend any resources, on or off line, where I can start to track the family down? I'm keen to try and take the family back at least one more generation, but I'm well and truly stuck at the moment! Thank you