Things to consider:
Cannot exceed 400 KB which includes both attribute name binary length (UTF-8 length) and attribute value lengths (again binary length). The attribute name counts towards the size limit. For example, consider an item with two attributes: one attribute named "shirt-color" with value "R" and another attribute named "shirt-size" with value "M". The total size of that item is 23 bytes.
BatchGetItem item maximum per operation
Up to 100 items retrieved. The total size of all the items retrieved cannot exceed 16 MB.
BatchWriteItem item maximum per operation
Up to 25 PutItem or DeleteItem operations per BatchWriteItem call. The total size of all the items written cannot exceed 16 MB.
Redshift vs DynamoDB:
DynamoDB table names can contain up to 255 characters, including '.' (dot) and '-' (dash) characters, and are case-sensitive. Amazon Redshift table names are limited to 127 characters, cannot contain dots or dashes and are not case-sensitive. In addition, table names cannot conflict with any Amazon Redshift reserved words.
Loading Data From DynamoDB into Redshift