He’s a designer (I hesitate to use the word ‘architect’), who has a reputation for getting credit for the ideas and work of others, and for projects with teething problems.
It’s pretty much unheard of for someone in the field to have a PA taking on that level of responsibility, and given his firm’s reputation, I suspect that the salary will be well below the going rate for other senior PA roles. The perception amongst Architects is that even though there is a horrific long hours culture within the profession, if you’ve got yourself in a position where you need someone to be your surrogate in your family and your personal life, maybe you’ve got the balance all wrong.
(he’s also expecting them to take on the role of a project manager for a construction job - that’s a fully qualified position in itself)