Well, he'll get paid JSA on the basis of a single person/lone parent with child under 18 so looks to be about £60/week according to this site:
http://www.direct.gov.uk/en/MoneyTaxAndBenefits/BenefitsTaxCreditsAndOtherSupport/Employedorlookingforwork/DG_10018757He may or may not get Child Tax Credit. I'd get onto the HMRC website to see about that.
No one can tell you how much housing or council tax benefit he might receive because that depends on your rent, the size of your home (and your council's criterion about how much space you need), but he should get full council tax benefit (and have to pay, say, about £20/month for council tax or so) and all or part of the rent.
Hopefully he'll get working soon.
Working Tax Credit is for people who are working 16+ hours/week and earning around £15,000/pa at a max - gross.
You may have seen what you felt were 'large numbers' on the tax credits site. Something to consider is that if you are getting Working Tax Credit, you must still pay tax and NI. So the £15,0000 max is actually about £11,000 net. And again, you have to be working 16+ hours to get that and it tops out at a relatively low rate of pay.
