Edwardian covers a lot of bases and 3,500sq ft is a huge house; roughly double the size of the average four-bedroom detached new build near me.
Fag-packed calculation but I don't think you'd see much change out of two hundred grand. If you're in a conservation zone possibly more.
Windows alone could be tens of thousands. Where I am (central Edinburgh) the tenements and townhouse flats in the New Town and West End often have big sash windows.
A friend of mine was quoted £13,500 to replace four windows of this type. Needless to say, they didn't bother, and just turn the heating up. It's cheaper.
My current flat (which is rented, so this will never be my problem) is about 2,200sq ft (for reference). There are 11 windows in total, six of which are almost 10 feet tall. And there are restrictions on what kind of windows you can put in, thickness of glazing, etc.
Just replacing the windows in my flat would cost more than £50,000 I think.
Would you be eligible for any grants or incentives? Here in Scotland there are government incentives and interest-free loans you can apply for to help make a home more energy-efficient. (Or to buy an electric car, as I discovered recently.)