SuperCharged

There's hunger, thirst, sickness, injuries and so on, but not resting. I think it would be fun and interesting if the player needed to rest in a bed (or something of that matter) to regain some strength. Additionally, in order to rest safely, the player should be able to barricade windows and doors with wood, nails and a hammer. What do you guys think?

I was thinking of a leveling up system, where the longer you survive, the more xp you get. Also, when you kill zombies you should get xp to level up as well. I don't think killing players should give xp because that would encourage others to just kill on sight, but I do think a leveling system should be added so others can gauge each other's skill (maybe also skill points given per level?). What do you guys think?

I really like this, and I think you're right. I'm just trying to think of ways a player may be rewarded for long term survival but everything you find and build is the incentive itself.

Yeah something like this is exactly what I was thinking, and hopefully the issue of players server hopping and killing others instantly will be fixed. If so, then barricading would be pretty cool, especially since zombies can already run through doors.

Exactly, maybe an HP boost or strength build after being attacked.

Not sleep, but rest. Like a minute or two max.