Are the numbers in the Book of Revelation symbolic?

There are some strange numbers in Revelation. For example: - The seven Spirits of God (Rev 4:5); - Exactly 12,000 are sealed from each of the 12 tribes of Jerusalem (Rev 7:4). - The blood flows out of the wine press for a distance of 1600 furlongs (Rev 14:20). - The wall of the New Jerusalem is 144 cubits (Rev 21:17 - YLT). - The New Jerusalem itself is a square – 12,000 furlongs in length and in width (Rev 21:16 YLT). (A cube in the KJV) Are these numbers literal or symbolic? If they are symbolic, what do they mean? For example, what does it mean that God has seven Spirits?