I will only answer one question to start the discussion.
""What are the most important personal skills for this job?""
Perfect knowledge of industrial design and have a very, very good knowledge of mechanics. These two things can be learned in 2 to 5 years, you need about the level you already have, but for example with a DUT in mechanical and production engineering. After that, you have to spend a lot of time dissecting all the existing mechanical systems (before the internet and youtube , I spent a lot of time at the CNAM Museum to see and try to understand all the mechanisms) and reproduce the simplest to the most complicated parts. After that, as long as you can , you have to change companies every two or 3 years max to see as many things as possible. It is by being confronted with the multitude of the existing and the future that we can fully express ourselves, after which individual intelligence will make the difference.
Kind regards
PS:
[HS subject On]
Between us, with such a background already acquired, there are certainly better things to do so as not to lose these achievements. I usually say that professional development is like sitting on a tripod, if you change all three legs at the same time you break your neck, on the other hand if you make each of the legs grow alternately then you will have a good progression. The other solution is to develop a fourth leg, which may lead to a weakening of one leg of the initial tripod, but you will have great certainty in your evolution. Nothing prevents you from having a chair with 6, 8 or 12 legs, but on the condition that you always have at least three legs of good value. Each new leg is not acquired instantly, hence the interest of the tripod ;-) Recruiters also look at the number of legs you have on your multi-legged chair and especially the solidity of each leg and the consistency of the skill of each leg. When they hire you, they say 'it's a good idea to find such skills, very good recruitment'" [HS /Off]
Unfortunately, there are no universal answers to your questions simply because of the variety of companies and positions. Simply the size of the company is enough to significantly modify the notion of autonomy and the extent of the skills required. You only have to look at the profile of the participants in this forum to realize this.
The training includes the design of 3D parts with Solidworks and Autocad from specifications, RDM, failure mode analysis, managing subcontracting, estimating costs, etc.