I lived in Belgium for almost eight years, and my wife and I dealt with a number of people throughout Europe over that time. We learned some rules of thumb that are usually applicable to French people and French speakers, when you are in negotiations with them.
First off, everything can always be renegotiated and brought back on the table, regardless of how many times you think that some issue has been permanently resolved.
So, nothing is ever really finalized there. Even if you get into a situation that has to be taken to court, you can still negotiate anything at any time. When they lock you up and throw away the key, that just changes who you negotiate with. If you think you got a bad deal, you just need to get a lawyer with a better reputation and suddenly the deal gets much better.
Second, everything is all about who you know, and did you go to the right school. If not, then there's really not much hope for you to break through the glass ceiling. Not unless you can find another way to get properly acquainted with the right people who can introduce you to the next set of right people.
Third, the Workers Councils are extremely powerful. Whatever you do, don't get on the wrong side of the workers councils. That means absolutely no overtime allowed, don't take your work home with you, and don't even think about annoying anyone who is on strike. And they will strike at the drop of a hat.
If things do go sideways for you at a job, the Workers Councils are your best friend. Before any company fires anyone or does any layoffs, there are massive documentation requirements the company has to go through, and in the case of layoffs they have to notify the Workers Council at least a year in advance of even beginning to prepare to take any action.
So, in your situation, I would be inclined to go back to them and see if they can sweeten the deal to your liking. Everything should be on the table. You've only seen their first offer so far.
Oh, and the work week over there is 35 hours per week, not 40. Seriously, do not get the Workers Council pissed off at you by working a single minute per week more than the legal amount.