@voxdominus Hi there 👋 I use Canva | Adobe Stock | Unsplash - I use Squarespace so I also purchase from Unsplash but I have my own account with Unsplash which you are free to use the photos. All are great and work well!
I still have one board that doesn't have a created cover - I find that the created covers for the boards work well for viewers and followers.
Glad you are here.
Hey! @voxdominus thank you for the links. Actually I never came across to these kind of articles, they might be helpful. But I don't think you should set boundaries to yourself, you can design some couple of pins and check out which ones are working for you. Just make it good looking, understandable and high quality. Good Luck!