Look at arbitration this way. Its a speedier end to the never ending delays that normal channels will make you go through.
In my personal experience, the arbitrators now the legal guidelines that can and can't be used. They will submit the outcome to the courts and it generally will get approved by the judge as submitted.
Nothing you are discussing in arbitration is really any different than it would have been in attorney driven normal proceedings. Just a lot less opportunity to lay smoke screens, delays and legal stalls to detract from the points you needed addressed all along.
It is up to you however to be prepared.
From the sounds and looks of it, you are.
It is faster for you to do this and a tactic that he can take advantage of to get this over with before all of this gets discussed openly in court proceedings.
Good luck. You're doing great. ( I must say he is making things way easier for you by his ongoing actions). :-)