Main question: How do I manually edit raster layers on QGIS 3.0?
Some context: I georeferenced Google Earth high resolution downloads on to QGIS, and was looking to do image classification for a study on urban areas. Everything I read suggested using ORFEO Toolbox, but my QGIS 2.18, which was supposed to come pre-equipped with ORFEO never seemed to work for me and QGIS 3.0 is incompatible with ORFEO. Then I tried the Semi-automatic Classification Plug-in (SCP) that is also recommended, but it doesn't seem to like my GE screen grabs because they only have 3 bands (everything I read says it should be 4 or more bands). Then I thought I might try just editing the pixels manually so that one color meant built-up, another vegetation, etc., which would take forever, but at least would be more straight forward- but I can't figure out how to edit pixels on QGIS (I read that the Serval Plugin would work, but it is incompatible with QGIS 3.0 and before going back to QGIS 2.18, I wanted to see if there were any other recommendations). Ultimately, I'd like to create a vector layer with an attribute table that has the %age of land-type per polygon (land-type percentages coming from the raster that I create from the georeferenced GE image).
I am using a MacBook Air.