Likely won't answer all of your questions but the below may be a start:
SLAs:
https://www.dynatrace.com/sla/saas/
This is the managed architecture but it is nearly identical to SaaS just hosted by Dynatrace in AWS (a few minor differences):
https://www.dynatrace.com/support/help/get-started...
General info that may be useful:
https://www.dynatrace.com/support/help/get-started...
As far as sizing for SaaS this would just be communication with support. There would be no documentation on this. For managed horizontal scaling is possible by adding new server nodes to the cluster.
James
