How do I defend my estate do I need troops in it to defend it?

Teammates could reinforce or you could shield.

Yes you do. But it is worth noting several factors. How much research have you done, not just in estate defence, but troops also; which troop type you are using, thence which commanders are manning the wall; wall level and troop level. These are all within your control. Another thing you can do is try to convert any free apples or crystals into items of the same in the market. One thing you cannot control is the force used to attack you. As troops are valuable, and take ages to heal/retrain, a good tip is to camp them out overnight in split armies. At least until you are higher enough than the usual quit level, typically sh17-sh18. At sh21 people stop attacking and start inviting!