Hey, this post is kinda old so I don't know if you'll still see this reply or want to play Terraria, but I'd like to do a coop playthrough as well. I only started really playing Terraria about 2 months ago but since then have beaten all the bosses, created and beaten moon lord on multiple worlds, and hoarded god knows how many items and just got my platinum trophy earlier this week! But, the game is pretty dead... in terms of finding people who still wanna play the game... which is a bummer.
I recently made a master mode world to farm one of the last things I needed for my plat then realized I wanted crimson instead of corruption so am planning on making a brand new master world... again
But yeah if you're still interested in doing a playthrough hopefully you see this in time