Depends on your map and how far away some stuff like silver or iron is from your main base.

Personally I have 2 main bases - one on the coastal meadows at the starting point by the Stonehenge trophy thing. I did Copper, Bronze, Tin and some Iron here - but a mountain was like 15 mins sailing away so decided to make a mountain base (in one of those round stone towers) there and did Iron, Silver and black metal smelting there too as plains and swamp was nearby there too. It basically cut a lot of hauling and now I have one of all top level items I'm really glad I did it that way.

I also have a bunch of other bases mostly for fun and storage - like a pillar top base with sea diving board and a flax garden below, but most other bases are small functional things just for protecting a portal.

Two portals in your main base is all you need by the way - one Called 'Home' that never changes name and the other 'outbound' you rename to where you want to go. New bases you put a Home portal in, portal home, rename 'outbound' to whatever, portal back from home, and change the new location from home to whatever you want it to be long term - and call it that on the map marker. Its a great mechanic and I'm personally really glad they don't make it too easy and allow you to enter portals with metal/ore as you'd only ever need one base that way and that devalues the 'exploration' aspect.

Hope this helps!