Using SmartThings for security is tricky because it’s a cloud-based product. If the Internet goes down, not much works and it does not have the ability to use cellular communication with a monitoring station. And all of its notifications to users, including you as the account administrator, require the Internet.
They do have an extra cost option where you can sign up with scout for monitoring ( but only for intrusions, not for fire.)
So it will work for some people, not for everyone. ( I personally have a completely separate security system and use SmartThings for convenience notifications like the guestroom window being open when rain is expected.)
As far as getting an alert from just one studio, yes, that will work fine, again provided that the Internet is working. One of the good features of SmartThings is it lets you set different rules for each individual sensor, it doesn’t just treat them all as one group.
With regard to your tenants, I would recommend giving them smarttiles for their controller. This is a very popular third-party app. It lets them turn on and off the devices you have made available on their dashboard, but they don’t have any account level capability.
Of course the question then is do you want them to be able to make up their own rules for when the lights go on and off, for example. If that’s the case, they have to have full admin access to the SmartThings account. So it can get tricky for a landlord. Smarttiles usually works fine for an Airbnb situation, but might not for longterm renters who want to create their own automation rules.
You can find some discussions on this topic by using the quick browse list in the community created wiki. Look in the project section for “second home.”