I'm planning to do a mod but i don't where to do some things

First of all, i'm planning to do a mod that makes sense in isaac's patterns, with new balanced items(not that q8 items), 2 new biblical characters(David and Elijah), new cards and runes, bosses and normal enemies, but i just don't where i do some things, i know how to programme in lua but what programs should I use for pixel art and other things?(I use vscode for programming).

observation: I don't know the pixel count of the characters tho.