Celtic Moment

I’m going to Scotland (hopefully in a year or so). I’ve always been fascinated with castles & the whole Scottish culture. What is the best time of year to go & what region is best? I’m really thinking of going to the Highlands. I don’t want to go to a big “city”–I want to visit the smaller towns & the countryside. I also want to stay in a small bed & breakfast. I would love to stay in a castle, but I don’t know of any available. What are some sights I need to see? Any help is greatly appreciated!