Matt,
The windows won't take long at all, about a morning for them.
The cladding is the time consumming part, I would say you will do it all in about 2 days.
In total 2 1/2 days max.
I do a lot of schools in Essex and I think you will be lucky to get any more than 2 1/2 days out of it, you will be surprised at how quick you can do the job.
Don't price yourself out of work, be realistic.
Darren