How can I do realistic seamless wood?

Use Advanced Wood https://www.youtube.com/watch?v=KoVsXAZra2g

Can't you download it? There are many free seamless textures of wood and other materials out there.

Substance Designer is the best way of making your own wood, especially if you are looking for seamless textures. It takes some learning, but the skill is invaluable.

..you can texture with out importing the model within substance dedsigner . yout gonna have to uwnrap model to apply the texture . within you choice 3d app . create texture on defualt cube .. ( honest view - i dont think unwrapping alway easy process )

unwrap with substance painter can sometimes take longer than building the model.. sure depending on the model . Hveing a low and high poly enable selection

do you mean that you want to make your own textures? i usually use photoshop for making tilable textures