I can't provide direct benefits advice, but the government site has links to benefits calculation tools here which should assist in at least getting a ballpark figure: https://www.gov.uk/benefits-calculators
If you are able to participate in mediation sooner than the court order anticipated, then it may be more effective to submit a C2 application asking for the hearing date to be brought forward as 6 months is a long time for an open ended mediation commitment.
In the mean time, if you have set up the MIAM and got a date for the first session, then you have set that ball rolling.
It's clear to me from the order that the court does want to look at the issues, but fairly, and wants you to have been through mediation first before judicial discretion comes into it.
I hope that this assists?
My view would be that an appeal is going to be time consuming and more stress - and I do think the order is reasonable as above, so to say that the judge erred in law or fact (i.e. grounds for an appeal) is going to be difficult to establish.
A straightforward application to bring forward the court date should remedy this.
Can I clarify anything further?