Hi Mastermapmaker
Don't worry I am a noob as well! I started recently and I am now working with the Mr Ink tutorial asset that is shown in your second screenshot. You can find the free Ziva assets here https://zivadynamics.com/promos/free
Mr Ink comes with the upper body ROM, so you wouldn't have to download that separately. For your own projects/creatures or commercial work you would have to model the bones, muscles and skin yes. Which you can do yourself or maybe you could work together with a modeller. I know that there are people who make models of écorchés that put their art up on artstation who you can ask if they are willing to help you out if you want to practice with it, I don't remember the names of any accounts but they might even be in other posts on here and if I come across any I will let you know of course.
I hope that helps, good luck!