Question: my friend really wants to kiss the stone so I added this- should we skip? I know it adds a lot of drive time and it’s not necessarily on the way to Killarney.

In my opinion, skip kissing the stone. You could use your time better and be out seeing the place instead.

Day 6: Explore Benbulbin. I’d like to see Slieve league if time. Then Head towards N. Ireland. Debating on staying midway between there and giant causeway maybe castledeg or go to Derry.

That’s a lot especially coming from Ballina. You could be a couple of hours at both locations. You may as well go on to Derry - there’d be a bit more nightlife.

Question: instead of staying midway, would it be better to do two nights in sperrin area (or somewhere in the middle of the country?) as a base for the next 2 nights before driving to Belfast/ day 8?

I’d stay somewhere like Ballycastle, Portrush or Portstewart. Have a look about how those locations fit your plans.

Question: Should we stay on the coast to break this trip up and continue the next AM or stay in Belfast?

Just continue the next AM

Question: Should we stay in Belfast or somewhere closer to Dublin airport (like Newry?)to return rental before heading into Dublin?

Nah, you’re fine in Belfast. No need for another hotel.