1.
Perfect, we have also assigned 50 custom fields to the product using core customfield.
You are following the right way of thinking, it can be set up normally in the administration.
2.
Why should it be like that?
Do you understand mysql and increment ID at all?
VM is opensource, you can program this feature or ask someone to program this special feature for money.
But keep in mind that even Joomla article IDs don't increment after articles are deleted

3.
Definitely.
Hire a developer to program V8m this way.
I don't want it in the core VM though - that's just your wish.
You can set the mandatory fields in the admin in the field settings - where is the picture of what fields you have already set and what you are not good at?