Packing up for the trip...

[Phil]

....as to the cagoule - I have one of those long Pipers cape (sort of a rubbery waterproof thing). Are they still worn in bad weather?

Weather is more likely to be showers and sunny intervals this time of year. You want something that folds up small to carry and put on if it rains. Unless you plan to wear a kilt full-time I would still suggest some lightweight pants. You may feel more comfortable in some situations wearing pants and don't be disappointed when you find that almost nobody here will be kilted. You may even get tourists wanting to take your photo!
As Jock says it gets pretty cold here once the sun goes down and you need something warm (and preferably waterproof) for the Tattoo. We don't get balmy evenings here. Otherwise wear what you like. It isn't a particularly military type of show and the audience will not be wearing any sort of military dress.
Regards your debit card, your bank will charge you each time you use it so best to withdraw a few large amounts rather than many small ones. Most places here accept the major cards - Visa, Mastercard, American Express - just make sure your bank knows you will be using it here as they may block it otherwise. Also make sure you have a PIN (4-digit) to use in the ATM's. I would bring along another card in case you lose one as it will be your only source of cash.
And one final word of warning. If a shop makes a mistake when processing a card transaction and refunds the mistaken amount before putting through the correct amount, your card issuer is very likely to not only charge you but also convert the amount at a worse rate as if they were buying sterling back. So check when you get back.