The barebones base defense is:

Ditch (or raised ground) to prevent enemies from reaching your base
Palisade to break LOS
Workbench coverage to prevent spawns in your base

Optionally, you should also make an entryway that you can easily get a cart through and you can also easily and quickly remove during a raid. I prefer to use 2 wooden gates facing a bridge or a staircase with a workbench nearby. Iron gate is much stronger but you can't easily fit a cart through them and it only takes a moment to remove a bridge or stairway that's been designed to be easily removable so it doesn't matter.

If I have a base in a particularly dangerous location I'll leave a gap in my entryway that's easy for me to jump over but impassible for the mobs. When I need to move a cart in or out I put down the final couple of pieces, move my cart, and then pick them back up.

Stone is good (as a means of defense and not purely aesthetic) for bases you can't fully enclose and/or need to be built while under attack but keep in mind that it's not invulnerable (and particularly weak to stone golems). Stone is also good later on as it takes a lot less collateral damage during drake/bat attacks and the occasional deathsquito swatting.