Email on your own domain does two things a free account cannot. It signals that the business is real, which sounds superficial and measurably affects whether people respond to you. And it means the address belongs to the business rather than to a person, so accounts can be created, transferred, and closed as people come and go. Somebody leaving with the only copy of a mailbox is a problem you avoid by never creating it.
The administrative control is the part people underestimate until they need it. You can reset a password, recover the files of somebody who has left, enforce two factor authentication, and remove access the day somebody leaves. None of that exists with individual free accounts, and discovering it during an actual departure is the wrong time.
The alternative worth naming is the Microsoft equivalent, which is comparable in capability and often better if you or your clients live in spreadsheets or need the desktop applications. The choice usually comes down to which ecosystem you already work in and what your clients send you. Either beats free consumer accounts for a business.
At a small number of users the cost is modest and it scales per person, so check the per user price against the tier you will be on rather than the entry figure. The one thing worth paying attention to is storage limits, which are the most common reason a business unexpectedly needs the next tier up.
Set two things up on the day you create it rather than later. Two factor authentication on every account, since business email is the reset mechanism for your bank, your domain, and everything else, which makes it the credential worth protecting most. And a recovery plan, meaning at least one other person who can reach the administrative account if you cannot, because a business where one person holds the only administrator access has a continuity problem regardless of how good the security is.
Create accounts as individual named addresses rather than shared ones from the start, since a mailbox several people use produces no record of who did what and cannot be handed over cleanly. Shared aliases for functions such as support are a different thing and are worth having, but they should deliver into named accounts rather than being a login anybody uses.