Yes that should be good.
Maybe put missions too at an NPC.
i was Searching more about MTA and i discover that it have protection from hacks and cheaters.
And when i played MTA on a server, The bots have a custom skin (Zombie skin) when you connect to server it Begin downloading the skins and All another things.
The missions i say like:
1st Mission (Level Needed - 1) = Find and Kill 20 zombies.(Reward=Xp - 50 Money - 100)
7th Mission (Level Needed - 4) = Go near Zombotech and find Clues about the Outbreak.(Reward=Xp - 300 Money - 600
10th Mission (Level Needed - 5)= You received a call wanting help, Make a Group of Survivors, Go to the Wang Cars (Doherty) and check if there is someone. (Reward=Xp - 1000 Money - 3000 Item Found - M4)
you need to wait a time at missions that wont are for kill zombies and All levels have 2 Missions.
And maybe we put for:
At day appear some zombies, but at night it explode from zombies, and headshot is kill at same time.