Hi @rikotacards,
First, a small clarification: daml start is a convenience, not a requirement.
Depending on how many separate Daml projects you are trying to coordinate here, your best bet may be a plain Bash script that runs the commands in the right order.
Running your script can be done with daml script. For the kind of setup you describe, you’ll probably want a separate script to allocate parties that runs before most other things (though obviously after starting the sandbox); since party IDs are hard to predict, I suggest looking into the approach @cocreature described here: initially run daml script with --output-file to create the parties, and then get those parties with --input-file for subsequent scripts / tests.
Does that help?