I’m not sure what these levels would be for, but we already have something similar which is a general leveling and economy system here: https://dtp.dark-gaming.com/
To login, use your character name and your password from when you did /register.
DTP allows you to wear different tags/titles, as well as use different username colors. To get these items, you’ll vote on https://terraria-servers.com/server/90/vote/ with your ingame name, and you’ll get a lootbox you can open. Voting is free and just helps our server up the leaderboard.
For zombies specifics on this, you gain xp and dp per round completed, with a modifier for each map(see here for all modifiers: Mathematics of the Economy).
For a more in depth guide to dtp, see here: Guide to DTP