you can use spriting apps,just use pngs ,or anything really.I mean is there a website you use
If you are okay with a more advanced sprite editor, you can get Aseprite. There are instructions to compile it for free on its github.I use piskel.com, it's a free online sprite editor that lets you able to sprite certain stuff! Plus, it's my level of balance between user-friendliness and the amount of features the app has!
But of course, that is just an option.
As of right now, sadly, yes.Do I have to have terraria on pc
DanmAs of right now, sadly, yes.