Thanks all!
Yup, I know about TechSoup, I didn't think they sell O365 licenses directly though, I thought they just direct you to MS as you can get the MS donations directly from MS.
Basically, thinking a little more about what I need to accomplish in 365:
Keep all emails for 2 years (company policy). Currently we are using a 3rd party filter/archive service for our on-prem Exchange server. I was thinking if we moved to Exchange Online we could possibly get rid of that and use MS services? I know there are retention policies that can be configured, but wasn't sure what level of 365 is required.
We have small departments, 1 handles applications that contain SSNs, the other handles payment processing (so they touch CC numbers, although our policy is not to store these - we use a 3rd party payment processor). I'd want to protect the data these users handle by making sure it's not leaked or shared accidentally while still allowing them to make use of the collaboration tools like Teams and Sharepoint. I'd also like to restrict any such data from being downloaded to a home device (editing in the web app version of Office would be ok). That's why I figured I'd need something more than E3.
Thank you all again!