What will the moon be used for and how big could moon bases be?
The main things that I can see as near-term uses for the moon are
1. Source of water for space operations that is many times cheaper than bringing water from the Earth. Lunar mining for water and ISRU for lunar cement. Fuel for satellites and other beyond earth orbit operations.
2. Moon as a destination for Antarctic scale science operations
3. Dark side of the moon for 100 meter or even kilometer size grand space observatories. Telescopes in a vacuum and can be made giant in one-sixth gravity and using lunar cement for structure.