Need Terrarian's help

I have no idea but bump for visibility.

Here you go.

Prepare to spend a lot of time fishing.

I'm not sure exactly how you can defeat the bosses using a fishing rod but if that's possible then good luck :P When I played Terraria I just used fishing as a distraction from the mining and treasure hunting.

Mmmmh do you mean that you want to start a new game, in which you do not fight bosses and monsters but just spend time fishing?

I am not sure you can accomplish that. Every night the monsters will come, and also the first bosses can happear even if you do not summon them.

Since you have finished the game (did you kill the Moon Lord or the Wall of Flesh?), now you could actually focus on isolating the two types of corruption and prevent them from spreading, building your own artificial lakes in different biomes, and fish there. The Angler can give you quests.