Ok, STBXH has pushed too many buttons now and I have decided its time to start contributing - if he can't be a proper dad, he can certainly put his hand in his pocket and help pay for them instead of paying money to go out! He contributes nothing 
My questions if someone can help if this:
Will CSA take into account the money I have to pay for childcare? Last month alone I had to pay out £600 for after school and holiday clubs.
I earn too much (I think) for tax credits, although I have just put in last years income and it said I was entitled to £1300 in tax credits, but then with my new salary from April this year, it says I am entitled to £300 a year, so presumably I will get the lower figure?
He is working randomly at the moment and when he does it is cash in hand, so I am guessing he will just claim he isn't working?
This is all new to me, so any advice will be gratefully received.
Thank you