Hi Sam,
I understand that you want to know the difference between Office 365 Enterprise E3 and Office 365 Small Business. I would like to share with you the summary of their general difference:
1) Cost
a. Small Business plan has two family services: Small Business plan P1($5/month) and Small Business Premium plan ($12.5/month)
Premium plan has an additional Office 365 Pro Plus license.
b. Enterprise E3 ($20/month)
Note: The price will change from the different regions.
2) Different Office applications
a. Small Business Premium Plan offers Office 365 Pro Plus application (some add-ons and features are not available)
b. Enterprise E3 presents Office 2013 Professional Plus application (the advanced version has all features)
Here is the Office application service description including the details about the difference: http://technet.microsoft.com/en-us/library/office-applications-service-description.aspx
3) More services which Small Business plan doesn’t have
a. ADFS and SSO service which is integrated with the local AD
b. SharePoint Admin center which can modify the site collection service, for example: TermStore and BCS feature
c. OneDrive for Business console to add the additional storage (The default is 25GB for each user )
d. The different SharePoint site and library limits
See the article below: http://office.microsoft.com/en-in/office365-sharepoint-online-enterprise-help/sharepoint-online-software-boundaries-and-limits-HA102694293.aspx?CTT=1
4) Enterprise E3 plan can add the CRM / Visio Pro / Project / Power BI online services together, however, for Small Business plan, we have to register a new subscription to use them alone.
Here is the detailed Office 365 service description that includes differences between all Office services:
http://technet.microsoft.com/en-us/library/office-365-service-descriptions.aspx
If there are any other concerns or anything unclear, feel free to let us know. We're always here for you.
Regards,
Rachel Zhang