All editors support working in Doom’s native WAD format, so files should be interoperable without issue. Some modern source ports have other formats like “doom in hexen” or “UDMF”, but we don’t need to worry about any of that, just pick standard, vanilla Doom format and it should be fine.
As for adding custom textures, that’s a bit harder if we want to keep compatibility with vanilla. Only the textures from the last loaded WAD are available, which means if we try to add custom textures we lose all of the vanilla ones. This can be fixed by importing all of the vanilla textures into our WAD, which will bloat it significantly, but is doable.
