Ariba,
There is no hard and fast ‘limit’ (unless you are thread number licensed).
The consumption of your integrations versus the capacity of your platform will determine when you are ‘out of gas’.
It is a good idea to have a methodology for determining your utilization and your potential capacity. Then monitor routinely so you can predict when you might hit the wall.
You can have a situation where a given process is lagging but have sufficient capacity still left on your platform. That is not an overall limit but a ‘local’ (process level) limit.
That situation usually indicates some re-architecting of the process needs to take place.
Assuming you have everything as streamlined as possible then you should be able to predict to some degree when you will need to do something before it becomes a necessity (assuming you are given the time to establish a methodology and do the monitoring and forecasting – most places think of that as a ‘luxury’.
One resource that has always been overlooked but frequently causes capacity issues is disk space. This has been true for virtually the my whole career no matter what platform. If the disk subsystem becomes constrained then the number one rule of computer performance comes into play ‘all computers, no matter their rated speed, wait at the same speed’.
Good luck!
email: jim.kosloskey@jim-kosloskey.com 29+ years Cloverleaf, 59 years IT - old fart.