Hello Ingo,
Unfortunately I can't answer all your questions, but I can share my recent experiences in setting up SSM72 in SAP CAL:
First of all I have followed the documentation which is in Evan Stoddard's blog "sap-solution-manager-72-coming-soon-to-sap-cal".
In my experience you will be forced to use the r3.2xlarge instance for Linux as the minimum instance when you create a SSM72 instance in SAP CAL.
Unfortunately this instance is no part of the free tier AWS. So you will be charged for about 1.71 USD (Region US-East-1) or 1.80 USD (Region EU-West-1) per hour of EC2 usage.
Quote from Amazon Web Services (AWS Case 1639905721):
"As per our Free Tier Terms, the use of r3.2xlarge instance is not covered for use under free tier. Only a t2.micro Linux or Windows Instance is covered for use under Free Tier. In addition, you are able to utilize up to 30GB of EBS Storage Volume Space under Free Tier."
End Quote
I have raised some threads about this subject:
3863984, 3865373, 3865854 and 3867560.
Hope this will clarify somehow.
Kind regards,
Frans Metselaar