I wonder if this is normal:

I seem to need 1 farmer for every 4 villager - unless I want them starve.

I have level 3 in farming, they fish, grow stuff and take down coconuts.

Out of 42 people, incl. children, 13 villagers are farmers - to me that seem a lot.

That's very normal. Of course, a lot depends upon the skill of the farmers. Master farmers are more proficient at feeding the tribe.