1 & 2 no, stuff will still spawn. I am not sure spawns are entirely tied to 'points' so much as 'put a grey dwarf out of LOS near player every 3 seconds' type logic.

3, the spawners are special things. They are physical 'buildings' that you can destroy that spawn the monsters. Again, the normal spawn is simply to create the monsters out of LOS near the player.

4. you can summon the spawn buildings for those specific enemy. And you can summon specific entities, like a troll. I don't know the codes.

note that workbenches, fires, and some other logic prevent spawning 'near' player structures, so building a castle will likely break spawns near it, to some distance. You can read the wiki on that ... there are a lot of details because most players want to keep monsters away.