My bible, which is a New King James translation, describes the size of the New Jerusalem as 12,000 furlongs high, deep and wide. All the conversions I have found tell me that 1 mile is equal to 8 furlongs. Therefore, 12,000 furlongs is equal to 1,500 miles. I notice that your writings on the New Jerusalem describe it as 1,400 miles high, deep and wide. Praise God there will be enough room for all of us whatever the size! I am just curious how you arrived at your 1,400 mile conclusion.
The New King James Version of Rev. 21:16 reads as follows:
“The city is laid out as a square; its length is as great as its breadth. And he measured the city with the reed: twelve thousand furlongs. Its length, breadth, and height are equal.”
The Greek word translated furlong in this verse is stadion, which is a distance of about 600 feet, whereas a furlong is 660 feet. 12,000 stadia equal about 72,000 feet or 1363.6 miles. Since the measurement is approximate many scholars round it up to 1400 miles high, wide and deep for convenience. But as you say, no matter what the exact measurement is, there will be plenty of room for all of us.