-as i mentioned in point 6 , enemy camp spawn won't be a problem even if your island full , it will be like garrison place when your generals back from adventure .
-will be great if bandits camp level/difficulty scale with the player level , not sure if that possible coding-wise .
-about destroying the buildings , this game need a vacation mode anyway , so this will solve the problem .
or another solution if you didn't login for 24 hour your production will stop and make bandits attacks stop aswell and this will solve the problem when the bandits camps spawn if your offline or online so player know for sure if he didn't login for 24 hour , bandits won't attack .
-about rewards .. where's the fun if there's no rewards.... sometimes we get bored of doing adventures , and having camps on our island that give loot/EXP will be great , so there should be good amount of loot depend on player level and camp type regular or leader