There is no limit to the number of daily on-demand backups that can be taken.
Up to 500 simultaneous table operations are allowed per account. These operations
The only exception is when you are creating a table with one or more secondary indexes. You can have up to 250 such requests running at a time; however, if the table or index specifications are complex, DynamoDB might temporarily reduce the number of concurrent operations.
There is a soft account quota of 2,500 tables.