Thanks for the effort, the nodes seem to run quite stable now. one nice to have would be an automatic rescale of the textures to a specific size, so one can add any textures to build an array.
and here is a solution for your other question, how to render an array texture with instancing:
RenderTextureArray.7z (3.2 MB)
needs the latest preview to run, it adds an easy way to manually add any kind of input value to custom shader fx nodes: https://visualprogramming.net