I was rooting around to sort my own hols.
but anyway, I live in Ireland
and can tell you sincerely that Shannon waterways and ajoining towns are all great.
To really see all the best of it I would qualify your question do you want to cover alot of ground motoring or stay in harbour for more than one night at a time.
couple of really nice spots are portumna athlone killaloe. these are well spread out. shopping
for the ladies . good provisioning
supplies and watering holes!
this will take you through a large open lake/lough . pretty scenery and many othe small marinas
and river exits if the fancy took you.
I hope this helps. any questions drop me a line.