Before you get too carried away, obtain a copy of McGibbon & Ross's five volume masterwork, The Castellated and Domestic Architecture of Scotland. Likewise, I'd suggest the possibly more easily obtained Living In Scotland and Living in the Highlands both by Lesley Astaire and Roddy Martine, as well as Scottish Country by Charles Maclean and Christopher Simon Sykes. The other "must read" book is The Scottish Chateau (I can't recall the author, and I can't lay my hands on the damn book) which is a superb analysis of the Scottish castle, as usually seen on shortbread tins.

Having lived in a "castle" for more than two decades (My great hall had a 42 foot ceiling, and in the winter it could get a bit more than chilly!) I would suggest you study up on castles before you take the plunge. If you are going to do it, I think you ought to do it right, otherwise you will end up living in what could jolly well look like a church that's been converted into a down-scale castle themed restaurant.

BTW, the last year I lived in the castle my heating bill was over $12,000 US. Reason #27 that I moved to the USA...