I'm impressed by your Irish skills! It looks like you have a wonderful itinerary planned so far, especially for Saturday and Sunday.
For your free day on Monday, there are plenty of good walking tours that you join in Dublin. Given your interest in military history, one such tour that I would recommend is the 1916 Rebellion Walking Tour
I have taken this tour myself and found it very informative and enjoyable. I'm sure you will as well. The tour begins at 11.30 am on Mondays and lasts for around two hours. You can book tickets on the above link.
As for travelling from Dublin to Galway, yes, you should be able to manage it in a little under three hours, traffic dependent.