Sorry for the delayed response.
homely it helped me incredibly because quite frankly I didn't want to hammer these things our directly with my ex. I also didn't want to deal with child access via solicitors. Yes it costs but it is genuinely for the best if you can arrive at a solution without solicitors letters to'ing and fro'ing.
The mediator will also give guidance.
Around common solutions used.
Around how access works.
Mine was exceptionally good in so much that when my ex would throw emotive issues into the mix, she would acknowledge what he'd said but help us focus on the practicalities.
I'll be honest child access was remarkably straightforward. All I asked for was consistency for the DC's and gave him as much access that he wanted. BUT (and this is a big but). I fundamentally don't have the concerns around access that you do.
He doesn't parent the same way I do, sure. And quite frankly he's not as emotionally stable as I am. But, I trust that he loves his DC's and it is absolutely in their benefit that he sees them.
The one word I will say about mediation is to try and leave the emotions at the door and deal with practicalities. If you have genuine concerns then you raise them calmly. The mediator has one role. To try and hammer out an agreement. If one party doesn't allow that to happen, then at some point the other party can tell the mediator that they wish to withdraw from mediation and that they have tried to mediate however it is proving challenging. They can then take that document to a family court for the court to sort access. Any seasoned lawyer will say that family court is really not where you want to end up about this. Decisions can be made that suit neither party.
I'm not saying this to scare you at all. I think the process is absolutely superb. And encourages parents to put the welfare of their children at the heart of these discussions (as opposed to pulling children into a divorce war).
But I think you absolutely have to accept that he will get access and overnight access to. I've seen nothing in any of your posts to indicate he shouldn't get that level of access. What do you need to do to be ok with that?