how do i use identifiers?

[NiLSPACE]

are there any other ways of warping players, perhaps through a plugin?

Yes, that's possible. You can use the TeleportToCoords function: https://api.cuberite.org/cPlayer.html#Te...ToCoords_1

oh, also, im struggling a little bit with setting the world spawn

To set the spawn you can use the core plugins' /setspawn command in game. It will set the spawn to the position you are at when you use it.