We plan to do the typical tourist things and are hoping to go late April 2016. I'm trying to plan it without a travel agency. Would like to stay in one castle and the rest b&b/hotels. We were hoping to go to Scotland for 5 of those days but I'm not sure if that is reasonable. Help.
Basically you need airfare, rental car or other transportation, gasoline or petrol (if renting a car), lodgings, food and drink, admissions to sightseeing venues and incidentals.
Most castle hotels are very expensive however there are a a few that cost a lot less. See my castle page for more info on that.
With the amount of time you have available, I would choose either Scotland or Ireland - not both.