I'm very glad to hear you now have a successful compilation and a successful upload as well!
Unfortunately, although I'm fairly knowledgeable about Arduino-specific things, I don't know anything at all about Marlin itself or about 3D printers. Even though I've helped many people to troubleshoot their 3D printer firmware updating problems, and even made some small contributions to the Marlin project, I have actually never even seen a 3D printer or even a 3D printed object in real life.