offered £600 a weeks work for £8000.
That is quite expensive as rounds go, unless it is excellent work. 2.5x the monthly income is more usual, 3x if it is VERY good (And sorry to be the bearer of bad news, but Justin is right, it doesn't sound that good!)
£4.50 as an average price is way too cheap. Even allowing for regional variations, you need better prices than that. I'd say a very minimum of
£100 per day is what you need, assuming you dont use wfp.
This works out at about 5 cleans per hour working 9-3 mon to fri
This is only possible if you are prepared to work in bad weather, which most WC don't. Also if you're buying work they will be used to a certain way of doing things and will be reluctant to accept changes as readily as your own customers. Also, you must take into account travelling time.
In summary, do I think you could earn £400 a week on this round - Yes, but it'll be hard work.
A better way would be to use your £8,000 to live on and pay your bills while you canvass your own work, at better prices than these. (An average price for a 3 bed semi should be more like £9 - £10)
If you dedicated just 3 days a week to canvassing, and got 5 houses per day (£10 each), you'd be at your £400 a week in just 2 or 3 months.
Buying work is always a bit of a gamble and it will never be as good as work you got for yourself.
-Philip