any tips on how to make it not look tiled? 
Use the Clone stamp tool or the patch tool etc…in photoshop. To check the seams, Filters–>Others–> Offset (by example if your texture is 512², then offset X=256 and Y=256)… if there are seams, you will see them. Then re-stamp etc… the thing, re-offset and re-check 
You could also make the material with a lerp between two versions of the texture, each scaled individually (via the UV pins).
With a “noisy” mask, blend between the two. (The alpha mask for ther lerp might also be a composition of different noise textures at different scales).
Its never goingto be really aperiodic, but the tiling will be less obvious…
first cut the large texture down the small original it originates from. then rotate this small texture in the unreal material function randomly.
I would avoid rotation as it tends to create moiree effects that are visually more impacting than any tiling…