Hire allies. More money invested into allies = more money made per attack. This really builds up a lot overtime, and is how all the lbers started out. In addition, building more guilds than troop builds (although you'll need at least 1 troop building) also helps you make more money.
There is no castle upgrade. There is nothing you can do to, with, or about it. There is no "castle code". If you are jb, you can swap files so it looks like youve upgraded it in the app. But if you scout anyone, they have a level 1 castle. Sory chu just gonna paste that now versus when he makes his thread xD