Lady Fly Fly
Maybe it wasn't running at the time but the 75 bus route from Slough bus station has a service that departs at 4:15 - arrives at Heathrow Central area by 4:45. Oh and route X25 from Reading departs at 04:00 arriving T5 at 04:38 Last bus home leaves after midnight.
As far as the other costs you cite. I covered phone in my original figures. Gas and electricity would be no more than £50 per month combined - my first purchase was a studio flat and I know ho w reaonable they can be on fuel. TV licence - £11 per month, Water about the same, council tax about £50. All told I reckon you'd have a total bill of just over £1000 per month in outgoings bar downroute eating. Mind you, if you are eating out to that degree, my allowance of £50 a week for food ought to be reduced.
Yes, it is tight, but doable and I've lived on less.