You might see a lot more if you hire a car as trains and buses are few and far between outwith the main centres of population. There are quite a few castles which have been converted into hotels - I've posted threads on two of them earlier this year - Otterburn Tower and also Sunlaws near Kelso which is still owned by the Duke of Roxburghe. Plenty of cheap flights between Scotland and Ireland if you book well in advance. Hopefully you will also have time to spend a few days in southern Scotland which is rich in castles and fortified farms, a legacy of the Border feuds. Ferintosh at Dumfries would be a good centre for visiting Burns Country, the Solway coast, numerous castles, sampling fine foods and whiskies and meeting some Scottish x-markers.