The team’s readiness to compete is square one. If you don't play hard you don't play should be the number one rule.
So how do you know how your coaching candidate performs if he or she does not have a body of work to go by?
Since you are obviously talking about Udoka, he has a 9 year body of work as an assistant in the pros and multiple years in Team USA. You evaluate that.
And you evaluate that the same way any competent HR person evaluates anyone. You see where they went to school(Pops University), you check with the school to verify education. You check with previous employers for references(SA, PHI, BKN, Team USA). You check with co-workers that the candidate gives you referrals for,(Tatum, Brown, Smart) and you have long interviews and delve into the candidate's ideas about the position, in depth knowledge of the candidate's knowledge of the company and requirements for the job, how the candidate sees themselves fitting in and how their personality would fit into the workplace.
People coming out of college get amazing, high responsibility and high paying salaried positions in businesses every day with little no experience doing that job. The hiring process isn't really much different between most positions across most industries.