We are serial doer-uppers and about to take on another (we hope).
There isn't a clear order for doing up. If you have the money start with the things that make all the mess, rewiring, installing central heating, if needed, anything structural. On the other hand roof insulation is a cheap thing to do, if needed, and will immeidately start saving you money,draft proofing windows, if not double glazed, and doors,
When we had children in the house, the first thing we did was decorate and sort their bedrooms. It reconciled them to the move and gave them somewhere to retreat to when other works took place.
As for furnishing, all of ours, bar the sofa, are secondhand. Do not forget your local auction rooms. I do not know why more people do not buy at auction. We recently paid £20 for a book case we would have paid over £200 for, if we had gone down the road to a good quality pine shop and bought it there.