Question in making a custom world 1.20.1

i am making a modpack that should have a custom world and i have some questio regarding that 1. how to make the create new world always create a new world with that particular world just refreshed 2.can i make the world custom in an area and outside that area is randomly gen if yes can i not do that 3. how to make something the endereyes point to the custom stronghold that i /placed i do not want it to be in the same place as the normal stronghold 4.how to make the structures respawn as the player can adventure into them again i have no problem using mods on forge or fabric