@Michael Knubben : The step-by-step images are approved! I hope it's of use! :) I posted them on my Artstation blog here: https://wendydeboer.artstation.com/blog
My general troubleshooting for advanced skeleton is simply to use incremental saving and save at begin/end of each step of the process. Get error like this - don't undo, just revert to previous increment and try again. Can also search the outliner and see if in fact two of those objects appear, delete one and see if that…
Digital tutors is best for beginners. There are lots of tutorials there. http://www.digitaltutors.com/ There are also learning paths in DT. Check it and it will help to learn step by step. http://www.digitaltutors.com/learningpath/