[PowerPC603]

First things first:
You need an account system.

You can choose between many alternatives like dini (really outdated and slow, not recommended), several other INI-systems and even MySQL.

Try to get something working that can save (and load) at least:
- playername
- password
- money
- score
- adminlevel
- kills
- deaths
- ...

Once you have that, you can start working on a login system (register and login).

When that's working, create some commands (zcmd is a good command processor) so you can make someone else admin, give them money, score, kick someone, ban someone, ...

Then you can add some extra commands to spawn vehicles, teleport players around, repair vehicles, heal players and such things.

You can also add systems for anti-hack purposes (really recommended).
Try to add server-sided money and score.

And after that you can add alot more.

As said before, it will take alot of time to get everything working properly without bugs, scripting errors and warnings.