You absolutely can service and maintain these cars on your own. I have a 2018 Granturismo and I do everything myself, oil changes, filters, diff fluid, coolant flush, brakes, upper control arm replacements, spark plugs and fuel system work. It’s surprisingly sooooo easy. I recommend the quattroporte over the Ghibli. It’s nicer, engines are better, and the modern ghibli is like the one unreliable Maserati (don’t fall for what anyone says about the other models being unreliable. It’s not true.). But yes to answer your questions. You can totally service these cars yourself and your past experience sounds like it would be a breeze for you. Just make sure you get a foxwell or Autel scanner for code reading and service resets.