Is it possible to:

1. Run commands on the players first time completing a certain course
2. Run seperate commands on every other completion of a certain course

1. Yes - run /pa prize [course] and set a command reward for the course.
   Then run /pa rewardonce [course] so that it is only given to a player once.

https://a5h73y.github.io/Parkour/part6.html

2. No - the prize for the course is either enabIed or disabled, so I don't think this is currently possible.

Regarding the second one, is it possible to do for example:

First time:
- 32 diamonds
- 3 commands (/money give, etc)
Other times:
- 1 diamond
- 1 command (/xp give %PLAYER% 300}

This is now possible with the distinction between "prize" event and "finish" event commands.
You could run "/pa prize (course)" then set a command prize, or "/pa setcourse (course) command prize (command)"
Then run "/pa rewardonce" to only give the prize once, every subsequent completion of the course would run the finish event, which could be set using "/pa setcourse (course) command finish (command)"