Ah! A 'silly question' specialist. That's great because I specialize in silly answers with overtones of sarcasm ....

  • MSM is mass storage mode (Boy, I bet you feel real silly now, huh?).
  • Sure, it's ok to delete it after it's been used.
  • I don't know the 'how' of device being triggered to use the GCD file other than it recognizes that the file is for a different version firmware than the one already loaded. The GCD itself is a bit like a self-loading EXE file, simplistically, in that it contains the same data as an RGN file and additionally (I suppose) a 'header' that directs loading of the new data to the appropriate regions.
  • RGN files are a 'stripped-down' version of a GCD and must be loaded manually in preboot mode using Updater.exe.
  • You should make a backup of the device's nonvol region at the very least regardless of how you intended to update it initially and keep the backup for the life of the device. Ideally, a full dump of all possible regions should be done at least once. Some are protected from copying but most aren't. The visible file system for MSM-capable devices is located in either rgn48 or rgn83 from recollection, so that very large region can be skipped if you have a copy/paste copy already of all files and folders. Possible region numbers are 1 to 255 but nowhere near all are populated and it varies between device models.

You'll have to insert your own sarcasm for the last 4 answers, I'm tired now.