There are two political decisions above all that this new administration will have to take in short order
Is it leaving the European Union without a deal? This will be the inevitable consequence of axing the Irish border backstop entirely from the Withdrawal Agreement. As has been promised in this leadership campaign (2)
If it's full fat no-deal then - short of proroguing Parliament (which won't work) - you are going to have to call a general election or a second referendum to get a mandate. Which one? (4)
To win this showdown, again you have to be ready to call a GE or a second ref on your revised deal to get it through Parl (5)