A easy way to check out how much troops he has at home when he’s attacking you use to look at the number of units he’s attacking you with and his military score. Military score is the number of resources you’ve spend building your army times 0.02. A hoplite takes 70 resources to build so it’s 1.4 points, archer takes 55 resources so it’s 1.1 points, etc. If you’re attacked by say 100 hoplites and 50 archers, that would be 140 + 55 points which equals 195 points. If his total military score is say 220 points, he can only have 220 – 195 = 25 points worth of defense left at home. He can of course have reinforcements from other players, but most often people don’t have that.

Being an active pillager is definitely the fastest way to grow, especially in the beginning. You’ll notice many accounts going inactive, and keep attacking them as often as possible, not more than 6 times every 24 hours though, in case they suddenly log on and report you for bashing.

Usually pillaging active player on your own island is not a good idea, it’s better for you that they grow as long as they donate frequently. An exeption to this would be players who don’t defend themselves and get looted by people from other islands frequently, it’s better that you get the resources than someone on another island does.
It’s important to have high level hideouts so that you can spy many possible targets at the same time, I usually just send one to each target and spy on their resources. If they have a lot I then spy on their military. It’s important to remember to blokade their harbour if they have war ships. Early on I usually don’t bother pillaging people with war ships, later on pretty much everyone does though. In the starting weeks of a new server you can usually just check out their military score and don’t waste spies spying on their military.

Second reason is too keep population growth high, a happy population grows more quickly, and during times of war when you need to recruit troops quickly it’s very important to be able to get a high population growth rate. Another thing when it comes to wine and war is that it’s much much harder to beat down a player with lots of wine cities, it’s almost impossible. Even if he loses all his troops he’ll be able to recover real quick since he’ll still have max population in his cities, he’ll be producing and consuming wine even if you plunder his other resources after all. A non wine city will have a much harder time keeping it’s population if it’s being plundered often since it depends on getting its wine sent from other cities.

If you’re in a peaceful neighborhood, being a peaceful player that and just sticking to yourself I guess having a mix of all kind of resources is ok, but for an active plundering player that risks being attacked back during night, wine is definitely the superior resource. If you worry about raids during night just set wine production to the same as you consume, stop producing all other resources, and you’ll wake up in the morning with lots of  gold and no losses. I’ll write more on this in my wine and plunder article.