Right, have finally read through the whole thread. Some of this may not be relevant now, but just want to give my thoughts. As others have said, access and maintenance are two seperate issues. The CSA dictate what he pays, not you and it is done on a set formula. They take 15% of his salary and whats left is his own. They will not care whether or not you "owe" him any money, that is not their concern. and as others have said, you had to buy a pram, cot, etc etc, so just take that £800 as his contribution to that and tell him to stick it.
He cannot dictate to you that you have to deliver DD to him. you could be agreeable and meet him half way, but that is up to you. It is HIS access to see his daughter and it is up to him to make it happen, not you. If you want your mum there, then that is your right and bugger all to do with him. If you do not want him in your home, then you go to a contact centre. All your emails prove that you are suggesting ideas and solutions, which he always turns down. The contact makes him look bad, not you.
I would not communicate with him now over anything and leave it until you have mediation. Mediation will be able to make both of you realise what is fair and what isn't and if he starts ranting on about CSA they will put him in his place. As for him now saying he cant afford to travel to see her, that is designed to make you stop the CSA. Dont do it. He is probably still buying fancy clothes and stuff. Its a question of priorities as I remind my XH.
When XH talked about moving to Wales, I text him and said "why don't you fuck off to Wales then and never see DD". meaning, you bastard, if you move to Wales, you will never see her. He chose to take the meaning as "If you move to Wales I will make sure that you never see DD again". Which was not what I said!
Try not to fret about it and remember, that the less time they see their useless fathers, the more time they have with us