to 1) Ok. Be reminded however that this has an impact on sound caching. Sound files in the the sound root folder will be downloaded and cached before the game starts. Sounds in the music folder are downloaded while the game is already running and played when ready. Maybe that was causing the issue.
to 2) Totally, you can add another animation to the explosive box called "Explode" for example, then put the explosion frames there.
Then you adjust your event accordingly:
On player collides with explosive box -> Explosive Box: Change animation to "Explode".
Then add another event:
On explosive box animation "Explode" finished: Explosive Box: Destroy
This should spare you a lot of tedious work.