I will create custom item and weapon sprites for terraria mods

No. I created this gig with the assumption that buyers would come from a technical background (especially that of the modding community) who simply need pixel art for their projects. Therefore, I expect you to be able to create a texture pack on your own if you choose to order this gig.

Depends on the complexity. As long as it isn't crazily complicated, I will be able to do it. We simply have to reach mutual agreement. Please just contact me first.

Yes, I can. I'm only limiting the gig packages to 48x48 px to streamline the process. Even then, the Breaker Blade is only 40x46 px, so I think that should be big enough. You can still contact me directly for custom sizes if you're developing a mod with huge swords, though.

Because every sprite in Terraria is resized to 200%. I have no idea why Re-Logic did this.

That depends on the size. For the most part I can make something up to 48x48 px, but anything bigger would take too much time, unless you're fine with that. I can't guarantee the animation quality either.

Yes, but it has to be under a certain size, since I don't do large sprites (excluding sprite sheets). Minecraft is especially possible due to its 16x16 textures, but I can only offer item and block textures without the 3D models.