How to work with asynchronous process from external client?

Hi! Dear Camunda Guru, please give me some advice about the best pattern of the task solution. My task is this:

  1. User make a request to the Camunda processor through own rest controller
  2. BPMN schema on a backend side consist of a chains of several asynchronous services
  3. Data will be ready for response to the User only when one final services on BPMN make it.

Every chain works not greater than 10-15 secs. And users sessions count is less than 500 an hour.

How to orginize work of the rest controller? Is it acceptable to force controller waiting of result in tha same call? Where a bottlenecks?