The number matters less than the structure. A business of one genuinely needs a single mailbox, and creating five addresses that all deliver to the same place produces five things to monitor and a false impression of scale that nobody is fooled by. Customers do not choose a business because it has a separate address for accounts.
What is worth having early is the distinction between a personal address and a function address. Your own name is where individual correspondence goes. A general enquiries address is where anything from a customer arrives, and it is the one that appears on your website and your listings. That separation means the business relationship is not attached to a person, which matters more the moment anybody else is involved.
Add a billing address once invoicing volume justifies it, which is usually around the point where a business customer asks where to send remittance advice. Larger organisations frequently want an address to file against, and giving them a personal one produces correspondence that arrives in the wrong place when you are unavailable.
Resist creating an address for anything nobody will monitor, which is the most common error. An address on your site that reaches an unchecked mailbox is worse than not having it, because customers use it and receive silence. Every address should have somebody responsible for it, and in a business of one that is a reason to have fewer.
Use aliases rather than mailboxes where the mail should simply arrive somewhere you already read. Most providers distinguish between an address that has its own inbox and one that forwards, and aliases cost nothing while mailboxes are usually charged per user. A business paying for six mailboxes it reads through one inbox is paying for the wrong thing.
Make sure the important ones are real mailboxes rather than aliases pointing at a personal account, because a mailbox can be logged into, backed up, and handed over while an alias cannot. That distinction becomes significant the first time somebody else needs access to the history.
Keep the naming plain and predictable. Something at your domain that a person could guess, using the conventional word for the function, is more useful than anything clever. Customers who lose your address will guess, and guessable is a feature.
Then check periodically that each one still delivers, since forwarding chains break silently and nobody receives a bounce. Sending a message from an outside address to each function address once a quarter is the whole test, and it catches the failure in this area that costs you customers with no indication it is happening.
Set the reply address deliberately rather than accepting whatever the system uses, since messages sent from a function address should usually appear to come from it rather than from you personally. A customer who receives a reply from your personal address will use that address next time, which quietly undoes the separation.
Avoid using a free consumer address for anything customer facing, since it signals a business that has not established itself and it cannot be handed over or backed up in the way a domain mailbox can. This is the single most common email error in a first year and it is corrected in an afternoon.
Add an address to your business listings and your website consistently rather than using a different one in each place, since customers copy whichever they find and inconsistency splits your correspondence across mailboxes you check at different intervals.