The only point of mediation is that you need to do it before going to court.
The point of going to court is twofold: to get a financial order to split the assets and for child maintenance (separate to the CMS process), and to get a child contact order, especially if you want to go for more than 50%.
As I posted a few days ago:
What is the timetable for the divorce? If you know a rough timetable, that will help you bite your tongue when he is being an arsehole. You will be gathering all your evidence in the meantime, then hit him with it in court (or mediation beforehand).
Keep Notes Of Bullshit
Ask your solicitor for dates and an explanation of the process (do some googling first to get a basic understanding).
You need to know how long this phase is going to drag on for.
Don't jump the gun. Lots of posters here are all riled up by what a total dick he is being, and can't wait to see you fight back and threaten CMS etc. We are all angry on your behalf.
Don't do it. Keep your cards very close and don't give him any sign of what you are doing or might decide to do.