Northstar
I work all over brum and have done many a school including some quite loacally to where you live, I am also a school governor, this gives me a insight to what their budget is.
The school will go for 3 quotes and the lowest will win.
If I was the governor looking at your quote, i would instantly dismiss it.
I think that the biggest problems you have at the moment are, you have never cleaned this type of property before and your predicting on how long it will take is slightly wrong, you do not have a wfp.
If it was me quoting for that school, I would do the following, I would have me on the outside wfping and have 2 day cleaners on the insides, after I had finshed the outside I would conduct a quality inspection of the inside and rectify any problems I come across.