Yes, there is a limit. If you received Cash, you and the members of your household must wait sixty 60 days after the Claims Start Date before becoming eligible for another Cash award. So if you file a claim for a $250 Reward on July 1st, you should wait until at least August 31 st before completing Challenges for another Cash reward.
We don't allow any sort of funny business to try to circumvent the rules, including using different addresses and accounts. You shouldn't create multiple accounts, share accounts with others, create accounts for others, or manage accounts of others either.