I'm sure I could try this myself, but I'm assuming someone already knows.

For vertex attributes: position,normal,texcoords,animation weights

Is it best to make these interleaved in one buffer, or separate buffers? If each attribute has its own cache of equal size, obviously it is best to keep them in separate buffers. Otherwise I guess just stick into one VBO and interleave all the data.

I believe the general advice is that interleaved is better. But, if you have some special reason for wanting separate buffers (e.g maybe you're updating positions on the CPU, but colours/UVs remain the same), then you should go ahead and use separate buffers for your dynamic attributes from the static attributes because there's not a lot of performance gain from interleaved.