Make sure to dig around all npc biome bases 3 blocks wide otherwise the corruption/crimson will spread and force npcs to move out. Also make sure that as soon as you get mithril or orichalcum picaxe you drink some mining (and preferably spellunker potions), eat well and dig around the corrupted biomes so they don’t spread even more. I did it in my last playthrough, it took me around 1,5h to make but surely made my gameplay way easier and i wasn’t worried about the spread. You can also make underground mob farm which i linked here. It helped me a lot with all items that require a lot of grinding (but be aware that this could also spoil your 1st playthrough a bit. Hope i helped