On the browser crashing issue, give Firefox a try, the last few versions of Chrome, have been a bit buggy. This is something we have seen, and Firefox seems to be a bit more stable right now. (I’m guessing you’re not using IE, which can be very unstable)
On deleting the unwanted resources, unused resources are automatically removed on publishing, so a quick publishwill remove them.
Multiple select, copy/paste, groups and layers are all coming in the next release, which should also cut down on the number of actions you have in your list. I’m really looking forward to that feature myself.
We don’t have a way to copy between scenarios, although we are looking at ways to implement that in the future, same for timed events
You mention downloading the cardboard app, do you mean the CenarioVR app?