Impacted Service Calculation using CMDB

[vgkorat]

Hi all,
We're working on an Event/Alert Management use case where we need to automatically compute impacted services whenever an alert is raised on a Resource (CI), but our instance does not have Discovery or Service Mapping installed.
Our CI hierarchy:
CFS (cmdb_ci_service_business)
└── RFS (cmdb_ci_service_technical)
└── Resource (cmdb_ci_hardware)

CFS → cmdb_ci_service_business
RFS → cmdb_ci_service_technical
Resource → cmdb_ci_hardware

These CIs are related manually today (no auto-discovered relationships/dependency maps).
What we're trying to achieve:
When an alert fires on a cmdb_ci_hardware record, we want the platform to traverse the relationships upward (Resource → RFS → CFS) and populate the Impacted Services (both technical and business) on the Alert/Event, similar to what out-of-box Impact Calculator does when Service Mapping is present.
Questions :

Since we don't have Discovery/Service Mapping, is it possible to still use the standard CMDB Impact Calculator / BSM Map / Impact Rules (cmdb_rel_type based) purely on manually created relationships, or is Discovery a hard prerequisite for impact propagation?
If manual relationships are sufficient, what relationship types (e.g., "Depends on::Used by", "Runs on::Runs") should we use between Resource→RFS and RFS→CFS to ensure impact propagates correctly in the CI relationship direction ServiceNow expects?
Do we need to configure anything specific under CI Relations → Impact Rules or cmdb_rel_ci_impact_rules for this custom hierarchy (Business Service → Technical Service → Hardware) to work with impact calculation?
Is there an out-of-box way for Event Management/Alert Management to auto-populate the "Affected CIs"/"Impacted Services" related list on the Alert using just these manual relationships, or do we need custom Business Rules/Script Includes to walk the relationship tree ourselves?
Are there any known limitations when using cmdb_ci_service_business and cmdb_ci_service_technical together in impact calculation without Service Mapping's automatically discovered dependency views?

Any guidance, documentation links, or shared experiences on setting this up correctly (without Discovery) would be really helpful.
Thanks in advance!