There is a danger of this post becoming too much for my head to processes at one sitting.
If you take 3 days in Dublin and do a couple of trips out from there then 3 days for Belfast, Antrim and Derry. You will get into Donegal on the 13th.
Cut out everything I have listed from the 15th and you have the basis of a really good holiday.
OK so you miss the south west corner under the Shannon but you can always come back and do the area South of the Dublin - Shannon estuary line next time.
Post a question on the Northern Ireland Forum for the 3 or 4 days in the North, ponaire will give better advice than you can get certainly from my moderate knowledge.
Sarnia G is a fountain of Knowledge as you can tell.
I am just Devils advocate and Cartographer with a list of bookmarks on the hard drive and more miles on the clock than the Star Ship Enterprise.
You will get a community feel and friendly banter plus a wealth of experience from the Ireland Yes forum.
Get a Michelin 712 map and pin it to an empty wall. get some coloured pins and have a play. Once you have some rough plan then come back to have it torn apart and reshuffled.