Regarding expansion of the "supreme" court:

12 is a better idea than 13. A complete tie would be equivalent to not hearing the case: no decision either way.

The justices would be motivated towards more face-to-face and other discussion, to avoid ties. There would be a greater chance to avoid extreme decisions. Instead of two highly polarized sides, some moderate factions could form, and lead to more moderate decisions.

Besides, 13 is unlucky.