In a battle, go to tactics and select a huge defense formation (preferably Half Moon formation) and when the required points are reached, purchase that formation and when generals and other infantry attack you, it does NOTHING!
If an officer won't join your side when you try
to hire him(or her), attack their fief and win.
After that they MIGHT be more willing to join
Level 4 Weapons
To get level 4 weapons, you have to have your weapon tech levels in empire mode to level 4 or higher. Then pick any battle and get 500 kills. After the battle, you will receive the weapon.