They are the same thing but Northerners tend to use quyển more while Southerners prefer cuốn. The former is the standard Sino-Vietnamese reading of 卷 while the latter is a further Vietnamisation of it.
Yes, quyển sách is 卷冊 and 卷 also gave rise to cuốn. In Modern Vietnamese "冊" (sách) means a "book" while "書/书" (thư) means "mail/letter". A library in Modern Vietnamese is
not "圖書館／图书馆" (đồ thư quán) but "書院/书院" (thư viện).