Dear OP,
I have been lurking with deep admiration at all you are doing. You must be in shock, his behaviour is truly awful. Well done for doing so much more than hanging on.
From your messages it sounds like he is trying to manage both you and your mil and quite skilfully too.
With you, he has been caught, he has not shown any remorse, he has proposed a separation on his terms (staying in the annexe) which you subsequently said you are unsure about and now he is proposing mediation (in a cleverly vague way) (Is that to push the annex, delayed timetable?). One thing is clear, he doesn't appear to have any interest in leaving OWWHHK and returning to the marriage (I'm sorry). Also that when he wants something he seems to come to see you, talk about it and then leave. He's moving fast to get what he wants.
Your mil reports he is giving the impression he's confused, that he might do mediation to repair the relationship (what she wants) and these messages are totally different from the ones he is giving to you. Perhaps he is trying to manoeuvre the situation into making it seem to your mil that it is you who is the one on insisting on ending the marriage rather than him.
It must be very hard for you to try to work out what's going on and I reckon he's probably aware of that and playing with your feelings to get what he wants while you are vulnerable.
What is more important is you want? What is best for you and what is best for your DD? You obviously have an immediate need for someone to do jobs in your home, to look after hens, walk dogs, cut the grass, cancel guests in the annex etc, but are these things sidetracking you and preventing you from concentrating on how you and your daughter are going to live in the future, split the assets, get the best settlement, etc?
It's incredibly difficult but before he manoeuvres you into fast paced decisions, why don't you slow it down a bit, wait until after he's been to Athens to talk to him again, so you have some space to get away, see if he is going to Athens and to work out what you need.
Even if you do these courses it will be quite a while before you build up your business to live off your earnings. What financially can you do for yourself and what will you need from him financially in order to maintain you and your daughter? And since your SSH (shit shirt husband) doesn't seem to think much about your daughter's future needs, you may need to do the thinking for the two of you. Is your daughter planning to go to university for example, will she have live with you in her 20s? What kind of support might she need and what can you get for him now while he is still (marginally) engaged?
Good luck, anyway, we are all watching with horror at him and admiration for you...