So far as the cottage is concerned it presumably already has residential permission & if you just intend to restore it I don't see why you need planning permission. However, if you want to extend it you may need it.
Building stables is another matter, & it's very unlikely you could do that without permission.
You will need to get the best guide you can from the council planning officer as to the likelihood of an application succeeding. If you want certainty before you buy you will have to submit an application, with the necessary plans, & pay a fee. But you might find the price increases if you then get permission.