You can ignore the warning, the UV are usually not overlapping (except if you are using the BFF unwrapper in Nomad, if your mesh has topological hole it will overlap badly).
In any case you can verify this in Nomad by using the “Inspect UV” option at the bottom, the UVs will be shown in the background.
As for the seams, try to bleed the texture a bit, by painting outside the UV islands in the 2d procreate view.