Run two scripts one after another with a systemd service

I have two scripts, what I would like to do is:

• at 1am, the first one runs
• once the first one stops, and this is a condition, the second one fires

So, should i use:

[Service]
ExecStartPre = script.py
ExecStart = secondscript.py

or

[Service]
Type = oneshot
ExecStart = first.py
ExecStart = second.py

man notes this:

Note that ExecStartPre= may not be used to start long-running processes. All processes forked off by processes invoked via ExecStartPre= will be killed before the next service process is run.

And my scripts can be long-running ones (some hours each).

Or is there a better way to ensure second runs only after first is fully-executed?

Also, this service is called by a timer:

[Timer]
OnCalendar=*-*-* 1:00:00
Unit = script.service

and i want only one instance of this running; even if the script.service takes 3 days to run, the next run should be reported to the next day after it finishes, at 1:00:00. Is this the default?