As I understand it, you can basically only have a single Australian/oversees coach on staff, other assistants and backroom would have to be 'domestic'. So who from SL would be choose to bring in? Arthur is unlikely to know this market for staff, so I would expect Blease to lead on this with a possible succession plan in mind for 2027 (if Arthur stays for 2 years).
I don't know that Walker and Grix are bad assistants, the head coach is the leader and person who gives strategic direction, the assistants should improve under Arthurs direction as much as the players do.
For those saying Athur is already the best coach in SL, let's just see how he gets on. Loads of reason for optimism, but also loads of rugby to be played, including a really tough fixture for magic. This group of players really aren't known for back-to-back performances.