I’m new to scripting, but this is what I’d do :
-You could create solids in your placeholder comps and then use “replaceSource()” to replace them with your clips.
-To get the clips numbers to match with the placeholders numbers, I’d use slice on the names, but if you have more than 9 clips, you have to name them Clip01, Clip02,Clip03, etc…
– I still haven’t messed around with comp settings, but you can get Item’s duration using “app.project.item.duration” I think. It’s a read/write for comps and a read only for other Items.
I hope this can help.