Am I planning too much?

Northern Ireland has good public transport Translink run all buses and trains if you want more information feel free to pm me

www.translink.co.uk

It does sound like you have a lot planned but it is hard to know without seeing the public transportation times. Taking a bus from Dublin to Killarney I think would take a whole day. Also not sure about your one day stops because with travel time you may have very little time to actually be in those places.
Some people like Rock of Cashel and some don't!
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I would take time in Kilkenny over Rock of C, if I needed to choose.

I loved the Rock of Cashel. It exceeded my expectations. It's a beautiful ruin with a lot of interesting details, if you take the time to look. The grounds are gorgeous, with many Celtic crosses and fabulous scenery in the background. It was my favourite of all the ruins we visited in Ireland.

It doesn't sound to me as if you have too much planned, although I didn't see all the places you are planning on, since I just had a week. We spent 3 nights/2 full days in Belfast, with one of those days involving a tour to the Giants' Causeway and other sites near the Causeway coast. We spent 4 nights/3 full days in Dublin, including two full-day trips--one to the Boyne Valley and area, and one to the Rock of Cashel, Blarney Castle, and Cahill Castle. (If I had to skip one of those three, I'd skip Cahill.) We had partial days in there, too, and made good use of them. So, I think you could possibly take a day from Dublin if you are worried you might be too rushed elsewhere.

We didn't see absolutely everything in Belfast and Dublin, of course, but I feel satisfied with what we did see.

Just returned from 14 day bus tour driving around Ireland, you are talking about a lot of bus time. It was just too much for me and I had a designated bus, not waiting on public transportation.
I loved Dublin, Kinsale and Dingle. I know Kinsale is not on your list but if the list changes try Katie O'Shea for music. Also, Dingle is known for its musicians. You could spend 3 nights there, pubs with music everywhere! Use it as a home base but enjoy your evenings too.

I did a three week tour of Ireland without a car many years ago. I bought a bus train pass to get around, and used certain towns as a home base to do day trips from. You will find some places on your list will be quite time consuming to get to by bus, and the train simply won’t help you in some cases. Before you set your heart on a particular itinerary I urge you to look at the bus /train schedules. You will find that it is best to stay more nights in towns that have good train/bus access so you don’t waste a lot of time waiting for, or travelling on, a bus. I spent four nights in each of Dublin, Galway, Killarney and Belfast. I also, was going to stay in Dingle, but after looking at the schedule for the bus I realized how much time I was going to lose just getting there. Instead I just did a day trip from Killarney. Remember, on days you have to use a train or bus to get somewhere, you will not have much time to get out to sights without a car because the guided day trips will leave in the morning before you get there. You need to really simplify your itinerary, and minimize the number of towns you stay in or you will be seeing Ireland from a seat on a bus. Cashel is worth the stop, but it is difficult to do it using public transit. I did it, but I had to take a train from Killarney to Cork, then a bus to Cashel. Then from Cashel I had to get another bus to get to the train to go to Kilkenny. And I had three weeks, you only have two. I was also able to make some other one night stops, but again, I had more time. Do a search for available day trips you may want to do, and use that information along with the train/bus schedule to determine which towns you want to stay in, and for how long. Remember, three nights in a town translates to only two days of touring.