British Pounds

Take money from the ATM when you land (or at a bank in town if the airport only has non bank ATMs)

And honestly, you don't need to withdraw a lot, since nearly everything is cashless. I pulled out 60 GBP for two weeks and that was plenty.

Depends on your comfort level and confidence you can find an ATM. Personally, I like to have a small amount of foreign currency in my pocket before I leave in case I need to get something before I can find an ATM. I don't get too much because usually the bank charges more than you would in the country or with a credit card with no foreign transaction fees, but for peace of mind, you absolutely could get some before you leave.

It will cost more to buy pounds in the US; the exchange rate is usually quite poor. If, in the end, you decide you want to have some pounds before you arrive in Scotland, don't buy a lot. You may end up not needing them, and you can get more easily enough if you do.

Important: When you use an ATM in Europe and when you pay for things by credit card, you may be asked (on the screen) whether you want to conduct the transaction in dollars or in the local currency. The answer should always be the local currency. If you opt for dollars, you'll be getting a much poorer exchange rate.

This query as well as the packing question (carry on vs checking) are just so personal and hence subjective, as far providing a definitive answer!
It is a fact that it's more expensive to exchange currency prior to leaving for your trip.
It is (likely) a fact that coping with a carry on suitcase or backpack in the airport can sometimes be a hassle.
But I always do both!
For me, it's worth the exchange fee (when balanced against the entire trip cost) for the peace of mind.
Ditto for the carry on.
At the end of a trip I apply any currency and coins to my last night in the hotel, or, pay for things in cash the last day.
Have a wonderful trip!

I always take a small amount of cash with me when I travel abroad. If you get it from an ATM it can spit out large denominations and since I mainly use cash for tips I prefer to have smaller notes which I can request at the bureau de change.

However, I’m in England. I’ve got 3 places I can change money within a 10 minute walk of my house so there is basically no hassle factor. I don’t worry about the exchange rate for such a small amount (€100 or equivalent).

remember that if you use a Scottish cash machine, depending on the bank, you will likely get one or another flavour of Scottish banknotes instead of what you might expect.

Many of us in the UK no longer carry cash or coin.

I spend 3-4 months/year in the UK. Much of that time in Scotland.

Last month, I withdrew 100 GBP out of the ATM. The last time I did that was two years ago.

More importantly, make sure your credit cards are contactless and if you haven't set it up already, look into Google Pay or Apple pay depending on your device.

Exchanging money at an "Exchange Bureau" will get you a terrible rate compared to an ATM machine.

Thank you for the many replies and great advice. I’ve been comfortable using Euros because I know I’ll use them for subsequent trips but really appreciate the feedback on BP. Cheers!