For easiest defense, I recommend a peninsula on the world map. An area surrounded by water on three sides.

Woodland is great for trees for your building/bow needs.

This way you only have to worry about defending from one side of the map, typically the map edge.

If you have passageways, select a new area/map.

Select a place far from the map edge, preferably near the water.

If able, make the area flat to work with.

Build the needed housing and beds for your characters to rest in.

Build a research bench to begin researching braziers. (Researching improved fire blankets and also the water buckets is advised to put out home fires, you do not need to be near water for water buckets to be used, nor do you need to craft either of them to fight fires.).

Build a woodworking bench, somewhere near your housing. Begin making short bows for all of your characters that do not have a long bow, short bow, or cross bow.

This part is important for your survival.

I recommend building a tower upon a hill near your houses.

Start off with it being made of wood, being in a woodland gives you unlimited wood to work with, just be sure to plant trees to keep up with demand.

The tower itself should be 5 stacks high and 3 blocks wide. (I am calling each floor a stack, when you place a building, it places two blocks high) A total of 10 blocks in height.

Place a door in the center of the tower.

Then build indoor stairs up the middle of the tower to the top floor, not the roof.

Build a balcony at the top across all three blocks.

Place a door at the height of the balcony for indoor/outdoor access.

Place more balconies on each side of the tower so that the balcony is 1 block wider than the tower on both sides.

Once you have researched braziers and you have sufficient materials from mining.

Build braziers on the balcony so that your archers can light their arrows to fire upon the enemy, as burning units helps decrease their max health, and can kill armored enemies simply by being on fire.

Anywhere that a lit arrow lands, will cause a fire. This can be to an advantage and disadvantage due to trees/sludge catching fire and injuring anything on that block.

Place all archers on the balcony for defense during attacks. Being far from the map edge will give you time to move your units into position.