Clothing, rain protection and shoes
Scotland has a lot of rain. It rains almost every day and that's normal there. If it's not raining, it's an exception! You have to be aware of that if you want to go there. Last time I was there, it was raining for two weeks. So rainwear is a must!
You need a good rain jacket and a pair of rain trousers that can hold the water for several hours. You can also put on your rain trousers over the normal hiking trousers if necessary. The "onion principle" has proven its worth.
I also recommend merino wool t-shirts. They're expensive, but you don't sweat in them. Moreover, they dry very quickly, there are no stains and they do not smell even after repeated wearing!
In addition, your clothes should have many pockets with zippers. There's always plenty to stow away when you're taking pictures outdoors.
You definitely need comfortable, ankle-high hiking boots!
Furthermore I strongly recommend so-called "Neos Overshoes". These are waterproof boots that you can put on over your hiking shoes. Rubber boots can also be used in case of need. The advantage of the Overshoes is, however, that you can easily pull them over the hiking boots. In addition, they are very flexible and can be folded into a small case. Nevertheless, they have a very stable sole.
When I was there, the ground was softened by the rain. There was a lot of mud on the hiking trails and on the meadows the water was partly 20 cm high. Without these overshoes I couldn't have reached more than half of the photospots!