Hi JP,
I would advise to use some form of Queuing. As of Mendix 9 an out-of-the-box Task Queue is available, you can make a loop which adds 1000 jobs to the same queue. In the properties of the queue, you can set how many processes may run in parallel. See example setup in screenshots below.
I see, you are using Mendix 8.18; would upgrading be an issue? Expected end-of-life of Mendix 8 is june 2025, so upgrading is needed at some point...