I have done enough research on this for myself and for options to put forward for clients.

Free Options are very limited.

Your plan of moving is a bit of a tough one as moving is fine but moving with all your email data intact without really experiencing email outage/downtime is kind of tricky ( as your plan is to move when your business grows/is growing - which means your email really is very useful )

So try to choose a service which suits you now and would suit you for a long time.

Yahoo! is a bit confusing to understand to from the above chart so read here https://smallbusiness.yahoo.com/email/compare-plans

Most services do provide Catch-all address^[1] so I would suggest choose one service and use the catch-all address till you can afford to make separate inboxes.

Zoho Free is a bit risky imo, but great if you are scaling and can handle the cost later. Free Plan is upto 10 members per domain, to add the 11th account you would need to start paying for all the 11 members based on the Zoho Standard Plan

About Google Mail the committed year we can add more accounts but cannot delete any account during that year without charge.

I wouldn't recommend Office 365 unless you really want all the other services they provide. Also Office 365 requires a annual commitment to sign up.

Yandex, I am a bit sceptical as its Russian.

There are a lot more services but these imo are very reasonable (if you want to add more inboxes in future). Good luck!

^[1] Catch-all address is an address that is specified to receive all the messages that are addressed to an invalid email for a domain.