hi Choco.. your Twunt doesn't get any better does he.... and never will... One thing that came out of my counselling was to accept that you cannot change the way that somebody else behaves
i.e. I cannot make my XH see his DD more than once a fortnight, or make him ring once a week.... It is hard, but when you accept that they are never going to change it removes a bit of stress.
My twunt pays around the CSA mark, and he did agree to pay for half of the school uniform, although he did try to backtrack on it.
What I did was to list everything that I bought, all from supermarkets apart from Clarks school shoes. The shoes alone were £32. You may not be able to get any more out of him, but maybe you could list everything that you buy and send him a copy, just for his information, although it probably won't get you anywhere. I emailed my twunt the spreadsheet and he did cough up half of it. I am going to do the same again this year, as he recently cut his money by £10 a week.
Yes you can get it cheap from supermarkets, but when they need 3 or 4 of everything, it does add up. Add to that PE kit, a decent winter coat, winter boots, trainers, wellies, socks, vests, pants etc and it does all soon mount up. I spent £180 on kitting her out with everything for the whole term, all as cheaply as I could. Since then she has grown like hell and I have had to spend more, which I have not asked him for.
as for your Twunt trying to represent himself in court, well he could make a fatal mistake that would cost him thousands, wouldn't that be a shame 
regarding guardians etc for the DC, I must admit, that I have appointed my cousin as guardian for my DD and asked that XH do the same if I go before him. He said he would consider it, but never got back to me on it. The guardian has no rights as the NRP would presumably have the DC to bring up, but you can appoint a guardian as somebody to consult over things.