There are a lot of ways to create seamless tiling textures. For years you did it by painting the center of the texture, offsetting the entire image by half on the x and y, and then filling in the empty space in the middle. Repeat that process until you have cleaned up any pixels that give away the boundaries of the tile.
I like to use processes to create art. A while ago now, I came up with a method of creating a certain type of stylized art. It involves a set of layers interacting with each other in specific ways, but beneath all of that sits a regular old layer of pixels that you (or more specifically, I) paint onto to create the final look.
When I’m creating new 3D models, I like to start with extremely sparse meshes and build them up gradually. The upside to working that way is that it is sort of like filling out a sketch or building simple forms first in a sculpture, and then only adding detail and refinement when you feel like the shapes are right.