Depends on your playstyle.

Lots of bases: If you like having strongholds all over the map, then you'll want to make a new base pretty much every time you discover a new type of metal. You'll want a meadows/black forest base for your bronze age, a swamp base for your iron age, a mountain castle for silver, a plains fortress, etc.

A couple of bases: Your main build times are when you enter the bronze age and when you enter the end game. It might be tempting to create a castle in the swamp or the mountains once you reach those biomes, but hold off and build a big castle in the plains for endgame. Some crops you need late game can only be made in the plains, so this is really the time to take everything you've learned from building and improving your meadows estate and make a biiiiig castle in the plains for your barley and flax processing, as well as your black-metal smelting.