Up to 925k stamp duty is 5%; from 925k to 1500 it's 10%. There's your first answer op.
£900k + sd @ 45k or £950 + sd £90k.
£945,000 plus my Conservative estimate £400k
£400,000
£1,345,00 (then add furniture to dress it and curtains/blinds will be at least £20k)
£1,400,000 to make it livable and dress it.
It will not be possible to live there for at least 9 months so at £18k min for an acceptable rental - costs now at £445k.
Property likely to contract by 15% over the next 1w months so it won't be worth £2m - it will be worth £1.7m tops in two years.
Providing all goes to budget: £1.7 x 5% selling costs so £1.6ish, less any interest costs - takes the margin to about £200k if there are no major unanticipated costs and if he's very very lucky.
Unless he is experienced and can potentially take a pitential loss of £150k to £300k on the chin I wouldn't touch it with a bargepole and my top price would be £750k in what is likely to be a volatile market with a lit of bankruptcies over the next 2 to 3 years.
I have only done it in an amateurish way in SW London op. I wouldn't touch this project. I made £250k on a structurally sound house and increased the sale price on another by £1m, spending respectively £220k and £350k. Nothing like the project this would be. Once a house is more than £1.5m they need top end kitchens and bathrooms and floors and curtains to achieve top end prices.