you want to change the number of users? Isn't that done via the server properties?
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Cast aside your festive doylaks: dragon stuff is about to happen.
One of the biggest issues when having a hunger bar is maintaining a limited supply. In games like "The Darkest Dungeon" or "Legend of Grimrock" you spend all your time adventuring you do not have a readily accessible supply of food. Making a hunger bar a feature which needs to be managed.
In games like Minecraft, on the other hand, you have an excessive quantity of food. Where it simply becomes an annoyance you must deal with. Since it is nearly impossible to ever not have food. You can run around with a sword and kill a cow, pig, or sheep and get meat at any time.
As far as I'm aware it is not possible to change the maximum number of players without restarting the Minecraft daemon. What requirements do you have? Do you want it to react to the tickrate or the amount of players on, etc.?
Oh NPCs. I think that's deceptive and not going to make your server very popular but ok. http://dev.bukkit.org/server-mods/citizens/
There's Citizens but that one isn't really designed for deceiving people. If you just search dev.bukkit.org for "NPC" I'm sure you'll find plenty.