I am not going to bore you with my personal views on bonsai pottery. So I keep it brief and point you to the references that are meaningful. This is by far the most insightful YouTube I watched about quality of clay and glaze to date:
https://youtu.be/KgsoSudK14Q?si=e_wFv5O3SuOzxpIQ
Are you contemplating to baking boinsai pots yourself? NaoTokutake, a reknowned American potter recommends digitalfire.com and you will figure it out.
Develop Sekka Hinoki in low unglazed pots (e.g. Japanese terracotta pots)
Try to overwinter the Sekka Hinoki in a frost free place. The trees that have overwintered free of frost will grow out faster and ealier than the ones that have been in frosty conditions.