"This is all so sudden."
Translation:Das ist alles sehr plötzlich.
Yes, ganz can be used for all, but a rule of thumb is to see if you can use the expression "the whole" in its place, and it still makes sense. Ich schlafe ganz nacht. (You can put in "the whole".... "I sleep the whole night") in the case of the sentence above, writing ganz is tantamount to saying "this is the whole very sudden". You see, that makes no sense, so we use alles which is the pronoun that can actually stand alone, and not alle, which is the adjective that generally precedes a noun. Hope that helped.