Main functional place in the game, players can interact with the map in certain locations to trade, save etc. As well as predefined trap areas which can kill off incoming hordes.
Saving could be as simple as sleeping in a bed, to save their character's progress, or maybe interacting with a console of some sort.
Trading could allow for purchasing weapons, attachments, upgrades, and equipment.
If a player dies, they will lose their entire progress until that moment, including survival time, inventory, and weapons.
Saving will allow players to return to the game with their inventory, from their previously saved game.
A primary server contains the main hub map, which will allow players to save, trade and travel to other areas.
Health shouldn't be fixed or determinable to any real degree of accuracy by the player, they should feel hurt from effects which impact their movement, reload speeds and the like.