This is something I've seen a few times
"Do you need the managers to be in an office to be successful or can they be remote?"
"Good question. . . well, if they are remote, they have to be the right person for the job <....>"
I mean… Yes? Everyone always wants to hire the right person for any job, you are not obligated to hire the first person that comes around just because it's a remote job.
You can send money to my PayPal because I may have saved you a consulting fee to ask this to some random remote consulting firm, which I will assume is a thing already (hey, I also gave you a free business idea right there)
Seriously you don't need to just pick a human at random and give them the job, that's not what remote means.
You always need to understand what traits you are looking for and how to check for them, and you also need to understand your biases. YOU NEED THIS IN ANY OFFICE TOO, come on.
I'll let the pros tell you about manager onboarding. I will however tell you, managers are just humans like your engineers. They need context, like your engineers. They need to have 1-1s, just like the engineers. Managers need to be onboarded and managers need good communication from their bosses, too (although manager onboarding even within an org is always a little different and harder!)