A lot of questions, but I will start with something you didn't ask, "determine agents for all steps in the workflow and store it in multiline WF-container" is not the only option, or at least not like this.
Yes you can determine the approvers at the start of the workflow, but their codes/titles and not specific users. so you will have a list like this:
01-Junior Manager
02-CEO
and not
USJOHN — Junior Manager
USXYZ — CEO
the users themselves should be determined by a rule. since the users can change in the process or the workflow.
Also, you do not have to determine a list of approvers at the start, you can use the workflow template ifs, cases etc. to determine the steps.
Now for your question:
1. you can transfer the specific table line to a single line element and them access specific fields:
ApproverList[&Index&]->CurrentApprover
CurrentApprover.User->User
CurrentApprover.Title->Title
2. should work the same as 1
3.Define as general and use a role to determine approvers.