In response to question 1, the maximum number of parallel workflow executions "tested" for WFA v2.X is around 38. Please note that this is the max tested limit and not necessarily the maximum limit itself.
Coming around to question 2, as mentioned above, there is no "absolute" maximum number of parallel workflow executions defined per se. However, if you try to exceed the max tested limit, you may end up with obsolete jobs.
Invoking a workflow on WFA that already has a significant number of job executions scheduled with a web service will absolutely have no effect on the service in terms of error, the web service will successfully invoke it and return a Job Id.
Once the workflow is invoked (immediate or scheduled execution), a corresponding web service can be used to retrieve the job status of the workflow execution using the relevant Job Id.
I hope that the answers suffice.
I have a couple of questions of my own based on your queries:
Is there a use case/s around which these queries were posted?If yes, please could you brief the same.
Are there any other limits in particular that you would be interested in?
Thanks so much for your quick response, this is exactly the information I was looking for. Our use case is more around understanding what the limits are so we know what our storage service needs to do in terms of managing how many requests it should send and have outstanding to WFA. Now we can let the developers know that they'll need to queue up requests internally if there are more than 38 outstanding requests that would go to WFA (or probably a bit lower so we don't overwhelm the WFA server and slow down all the jobs).
At this time there are no other limits I can think of that I need to look into.