what type of cutscene are you talking about, intro, outro,
You simply create the script that runs your cameras then if an intro type cutscene, run the file at the start of the mission from the init.sqs
or if an outro run it from the endgame trigger
If its a cutscene that is run when some event occurs, then have it run from a trigger when the triggers condition is met
I would not use "disableuserinput" as this often leads to clients being unable to regain control of their keyboard without a reboot even if you re-enable them with "disableuserinput false"