I just ran a test in one of our HubSpot Portals and some of the [most useful] functionality is available for Sales Pro users NOT Service Pro Users.
You still have all of the Properties, and the Target Accounts Dashboard, but there are some features that need the Sales pro license to set Stakeholders and Roles.
If you turn on ABM you can't turn it off again.
Happy to do a screen share if you want to see the features.
You will need to enable it to add new properties, then a bit of work to categorise your Contacts.
Have fun
Mike
Here to learn more about HubSpot and share my HubSpot Knowledge. I'm the founder of Webalite a HubSpot Partner Agency based in Wellington, New Zealand and the founder of Portal-iQ the world's first automated HubSpot Portal Audit that helps you work smarter with HubSpot.