Your base is where you can store equipment and items, as well as hide out in a safe spot that only you (Your party) can access. Though having a camp-base is free. having any structure as a base will cost some currency.
A two bedroom apartment: 2000
A small building/house (up to 5 rooms): 5000
A large building/house (Up to 12 rooms): 8000
A complete custom building (Any number of rooms): 10000
The amount of items you can keep in each varies as well.
Rough Camp: 5
Two Bedroom Apartment: 10
Small building/house: 30
Large Building/House: 50
Custom Building/House: Unlimited.
The only other things needed in your base is who occupies it, and a description of the interior, and if the base is a building it'll also need a location.