We did mediation because my ex didn't want to go to court...because she didn't want things to come out. In my state, there is no separation agreement so I can't help you there.
You'll settle custody, finances, etc. The goal is to find a truly impartial mediator, but that rarely happens in real life. You will need your lawyer, as he/she will work in your best interest and protection.
One thing I've learned is to not bend to her wishes on the hopes of the thought that somehow appeasing her will make her change her mind. This is nothing but business, I'm afraid.
I can't help on the SA. But I can on mediation and will talk anytime.
There are moments in this life when you are so confident in the rightness of your actions, that not even for a second do you consider the option that you might be wrong.