Making Ballistas is the biggest offensive step you will make. Once there you will need to set up an NPC farm rotation. You will want every bal you own farming npc's at least 3 times per day. 50 bal and 50 tran is enough for your first lvl 1 npc and will get you rolling. Your best farm is on lvl 5 npc's. If you attack with 350 bal and 200 trans (use a hero of at least 85) it is a great way to build resources fast, along with awesome XP for your hero. NPC cities regen all of thier resources after 8 hours. Don't wait the full 8 hours if you have Bal and transports sitting around. Attack attack attack. I built several npc cities in all directions of my cities, what I do is go south in the morn, west at lunch, and north in the evening. If I can I send out 6-9 waves per city. I send out every last wave I am able to.
lvl 1 npc ------ 50 bal 50 trans
lvl 2 npc ------ 75bal 75 trans
lvl 3 npc ----- 150 bal 125 trans
lvl 4 npc ---- 300 bal 170 trans
lvl 5 npc ---- 350 bal 400 trans
You will take losses usuing these numbers, if losses scare you then send more bal. I send this amount because my farm rate of medals and hero XP is really high usuing them. I recoup more than enough to keep my army building and replacing my lost units. I rarely let resources sit in one of my citites. The way I figure it is if I have alot of shit laying around ppl are more apt to try to raid me. These #'s are from my own trial and error, I find the balance of loss, xp and loot to work well for me. Adjust as you see fit. The key is just to attack attack attack. Mmmm I love war.
If you need help building NPC cities talk to any officer and we will help. Don't build to many below lvl 5 though as you will regret filling your area up with lvl 1-3 npc cities. Rock on.