Northern Ireland and Northern Republic of Ireland itinerary help

For our similar trip, we took the train Dublin to Belfast, spent all day in Belfast, then evening train to Derry. We used Derry as our base. Rented a car and spent a day in Donegal. This was not nearly enough time in Donegal, and we did not venture into Sligo. A day in Donegal was just scratching the surface. Spent the next day in Derry then morning train back to Belfast and Dublin. You appear to have a car the whole time, so you will be more mobile. Staying towards Dublin but not going into Dublin? Perhaps Skerries or Howth?

Just got back from NI from 5 night tour put together by a Rick Steves' guide who also has his own tour company.

In NI we hit Dunluce castle and then went to Leo's Tavern-- from wikipedia:

Leo's Tavern (Irish: Tábhairne Leo) is a restaurant and pub in the Donegal Gaeltacht, known as the home of music artists Clannad, Enya and Moya Brennan. The pub opened in 1968 and held Irish traditional music sessions nightly, becoming the musical starting block for the children of Leo Brennan, the pub's founder.

Call ahead to make sure you visit when they have music. Our guide did and it was delightful.

Between Dublin and Belfast, we stopped at Drogheda, County Louth, Ireland and looked at St. Oliver Plunkett's Head
St Peters Church and had a bite to eat.

Belfast has great music, and I'd recommend starting at McHugh's Bar. We just spent three days in Belfast, one day in Portrush (disappointing), then to Dunfanaghy (FB pages all fibbed about music). Donegal has great music at The Reel Inn.

Our next trip might be looking for a Donegal/Dublin waypoint, and Monaghan or Cavan are candidates, although never been to either. Westport had great music at Molloy's, and could be a clumsy way stop to Dublin.

You could do Belfast - Donegal - something - Dublin or drop the something and stay in Belfast two nights.

I'd be interested what was disappointing about Portrush? I am local to Portrush and Portrush is great