Minecraft – way to find which version a Minecraft world was created in

The world data, which also includes player inventories, is saved to a folder in the current working directory of the server.

The name of said folder depends on the level-name setting in server.properties, and defaults to world. Thus, you can start a new world and toggle between the saves by simply changing this setting.

Vanilla server commands related to saving/backups:

• /save-all - forces the server to save.
• /save-off - disables saving. You should definitely execute this before making a backup of a running server to ensure that the server doesn't save while you're copying, which could result in a corrupt backup.
• /save-on - re-enables saving.

Yes! And very easily, too. Profiles allow you to tell Minecraft where to store all its files by changing the Game Directory option in the profile. Just add something memorable onto the Game Directory (such as 1.7-snapshots) and that profile will never see your existing worlds.

How this works is, setting this to a different folder than the default .minecraft folder makes the game keep an almost entirely separate Minecraft install in the specified folder. (The only thing it doesn't keep separate is the game code itself – this is still drawn from the .minecraft/versions/ folder, which as you've found works just fine and doesn't compromise firewalling different installs.)

I use this myself to maintain multiple private modpacks separately from the main Minecraft version, and they co-exist perfectly and peacefully within the official launcher. It means that there is absolutely no danger of accidentally opening a modded world while running vanilla Minecraft (and thereby destroying the save!) or vice versa. I make it easy on myself by simply adding modpacks/[name-of-modpack] onto the end of the default Game Directory, which neatly stores all my modded Minecraft stuff in a "modpacks" folder within my .minecraft folder.