You might like to take a look at Parallel::ForkManager. Its DESCRIPTION starts with:

"This module is intended for use in operations that can be done in parallel where the number of processes to be forked off should be limited. Typical use is a downloader which will be retrieving hundreds/thousands of files." [my emphasis]

It then continues with:

"The code for a downloader would look something like this: ..."

The code it shows uses LWP::Simple but could probably be adapted for your Mojo::* modules. I've never used Mojo so that's very much a supposition on my part (and not something I can help you with further).