@bouchacha:
I usually like to get my second base going once I've filled out the brainer ranks in the first base. As soon as you can make barracks and workshops, its time to get stills up in a couple bases to start making cash from Grog and Apples. I let the runts at the first base continue supporting operations with guns, ammo, armor, prisoner processing etc, and when they are idle making cash. The 2nd and 3rd bases are definitely placed with an eye to radar coverage, and I like to keep them within electric vehicle range of the main base so the strike team there can prosecute any contacts generated by the other radars. Once these bases are making cash, I'll start expanding my global coverage, targeting the remaining land masses and finally the poles. 4th or 5th base will also become a manufactury with the goal of having a Factory there, and probably Printers in my earlier two. Sometimes both. I'll build a couple of the bases out as interceptor bases with 5+ hangars, and trained pilots (firing accuracy, reactions, and high bravery (90-100 if possible)) with low voodoo strength.
I think building a second base as soon as you get large vaults is a good idea. You need a place to store your stockpiles of soylent, apples, scrap metal and courtesans. And if you start intercepting you'll have even more garbage.
Personally, I never get large vaults. Early game, I get a vault in every base I have, then make up storage with workers. Hanging onto bulky items is not worth the effort (can be purchased easilly). By late game aside from an Armored Vault or two, almost all my storage is provided by Slaves, Farmhouses, and Servitors. Most of my bases have negative space.