It's so exciting you're thinking of going on your first trip at the end of the year, and I'm so happy to hear you've chosen Ireland as your destination! :)
If you'd like to travel by public transport
, you can hop on a bus at Shannon Airport to Limerick, and from there choose to travel by bus or train to Dublin. The train is a wee bit faster (about an hour), but when you travel by bus you get to see a lot of the lovely towns along the way.
Transport for Ireland has a helpful Journey Planner
that tells you exactly which bus to take and where to switch services. You can also download their app
so you can check everything while travelling.
It sounds like you've got most of your itinerary all planned out, but if you'd like a few more suggestions or tips, check out these Trip Ideas
. You can also find more information about the current situation around Covid-19 on the Traveller Health page
. At the moment the authorities advise against all unnecessary travel but keep a close eye on that page for updates.
I hope this was helpful, but please let me know if there's anything else you'd like to know! :)