Not rise to level while before increasing the max their popularity and always using money from duels.
Not is good leave the money in your account, because you will lose it when challenged by someone stronger. but...
if you want to leave to accumulate much money, combine the maximum of emeralds for buy POPULARITY BONUS AND ACTIVE IN ALL, or use your diamonds , buy bonds popularity to the fullest and leave active in this time. is very important active popularity bonus if you want accumulate and win money.
Remember that the diamond helps improve because it makes it much easier for you. Always try to be buying and using in their improvements.
Engagement parties will give you emeralds, experience, bonus and money in the missions, participate ! will help you a lot.