Sonic Mania modding help

After playing some pretty amazing Mania mods, I've really gotten into the idea of making mods myself. I'm probably going to start with sprites for Badniks, objects, and GUI, then start graduating to level mods. How do I do these level mods especially? For sprite mods, do I have to use GIMP for them?

My early level mod ideas are mainly changing graphics for stages (Stardust Speedway Act 2 into Stardust Speedway Good Future, Hydrocity into Aqua Planet), with later ones being Chemical Plant into Launch Base and Green Hill into Botanic Base.

 

You should probably check out the Mania Modding Discord.

 

Thank you! <3