For Security Management information (objects, etc), you need to query using the API or using CLI-based API commands.
What I pointed you at was the one that has the information separated out so you can import/export just the information you asked for in a relatively easy-to-consume format (CSV).
The Python Export/Import script (findable on the community) gives you everything relevant to a given Policy Package.
For the larger issue of documentation, problem is: it's not clear to me what problem the customer is actually trying to solve.
Even so, I suspect the answer is not contained in a single document as you've presented numerous scenarios.
For backups of your Security Management (and related items): https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solut...
Can you restore a migrate export in Smart-1 Cloud? Yes, but you need to use the correct migration tool.
See: https://sc1.checkpoint.com/documents/Infinity_Portal/WebAdminGuides/EN/Check-Point-SmartCloud-Admin-...
Management HA is covered in the relevant Security Management admin guide.
Partial copy of configuration from one management to another? Yes, possible using the API.
Which one is appropriate for the customer? It depends.
In general, we recommend employing multiple backup/HA strategies as it gives you multiple recovery options in case something goes pear-shaped.