Seebeck Coefficient variation with Fermi Energy at different Temperartures for the Same Material

Question

So we have been recently introduced to the Seebeck Coefficient in thermoelectrics, however, I had some questions on it, and I kept finding contrasting information online, maybe because I don't know where to look, however, here are my questions:

1. How should the Seebeck coefficient change with temperature at different fermi energies of the same material?

2. What is the relation between the Seebeck coefficient and the thermal conductivity of the material?

3. Physically, what is the reason that Seebeck starts off negative and tends to zero?

Any help would be much appreciated. Thanks!