If this is your first plane, then you might want to go with something more forgiving, like a trainer.

Anyways, ive never used hot glue on airplanes before, but with this type of foam, thats probably what I would use. I don't think I would use CA on that foam.

Your LiPo battery will work fine.

And the gearbox is fine too. If you crash hard enough, anything will break. It will be able to hold up to normal use.