You can create templates with 4K videos, as 4K stock videos are available. 4K stock videos are easy to spot as they are tagged 4K when browsing through the stock video libraries. The tag is besides the video duration.
As 4K videos are generally used for digital display systems. They work best with landscape digital display (16:9) or portrait digital display (9:16) designs.
4K video download purchases will not earn you additional royalties.