According to the section Workflow limits in Software boundaries and limits for SharePoint 2013
Maximum workflow definition (xaml) size
Description: Attempts to publish xaml files that exceed the size limit will fail.
Max value: 5,120 KB
Limit Type: Boundary
Workflow variable value size
Description: The maximum amount of data that can be stored in a single workflow variable is 256 KB. Exceeding this limit will cause the workflow instance to terminate.
Max value: 256 KB
Maximum depth of a workflow sub-step in xaml (workflow complexity)
Description: here is a hard limit of 125 for node depth in xaml. The maximum value of 121 levels accounts for the default activities (stage, sequence, etc.) that SharePoint Designer inserts automatically.
Max value: 121 levels
Limit type: Boundary