[LarzI]

Ammunation-stores are hard-coded into the game. I am not fully sure if it is possible to remove interiors, but at least you can try, using https://sampwiki.blast.hk/wiki/RemoveBuildingForPlayer

Creating NPCs is easy! Just browse the tutorials section - there are tutorials out there!

Checkpoints are even easier - just use a streamer or make your own "streamer".