Is it enough to backup the wallet when it is created or should they be backed up every so often. I am guessing it should be enough to back up once for every account but do not know much about cryptocurrency and this technology and wanted to be sure.
backup your wallet just once, you need only to preserve the private keys '
keystore' and also remember the password you've set.
read : How do I backup my ether accounts?
This depends upon the no. of accounts you create/use. Each account will have a unique private key stored in the
keystore folder. So, if you are operating with a single account, you need to backup the corresponding private key only once. This key won't change over time.
But, if you keep on creating new accounts, new keys will be generated(one for each account) and the ideal solution is to backup the
keystore folder every time you create an account so that the new key pertaining to that account will be safe. However, this is not operationally efficient. So, there are different types of backup. See differential and incremental backup.