I don't know if it make a difference, but you should run 'gradlew eclipse' after 'gradlew genEclipseRuns'
Also, the root of the Eclipse project would be the same folder where you extracted the MDK (...\Mods\Fluxed Machinery)
Don’t use that... that will break completely for anything that isn’t 100% standard. In 1.12.2 you would use RenderItem#renderStack. I’m not sure what the 1.14 replacement is, but it should be pretty easy to find by looking at the ingame GUI renderer or the item group renderer.