To switchover from Google hosting the mail to hosting it on Office 365, you'll need to make some DNS changes (on the domain registration). You can do that easily yourself. You'll need a mailbox license in addition to the software licensing, which I don't think you've considered the cost of.
OneDrive (and Teams) are a great way to store/share files and have them accessible on any device from any network anywhere in the world (including your mobile phone) and collaborate. Outlook and Word/Excel dovetail very nicely into OneDrive, too.
At this point, I'd suggest starting with the 365 Business Standard license for your two users. You can easily add more users later as necessary. Be sure to turn on MFA, too, for added security!
For my own business, I use AppRiver (recently purchased by Zix), for my O365 hosting. You can use a reseller like this instead of buying directly from Microsoft. The reseller charges about $1 more/month, but you get free 24x7 US based tech support. I highly recommend them as the 2 times I had to call for tech support in 7 years, they were very helpful and well worth that extra $1/month. I'm not sure what their current prices are, but they should be able to talk through your needs and devise a custom package to suit your needs. Yes, take this with a grain of salt b/c I'm already a customer of theirs. Give them a call and see if they're a good fit for you.
(I've worked in IT for over 25 years, so if you'd like some help, feel free to PM me.)