You could use SQL to find the name of the person who first approved a PO.
The SQL below will tell you that. While a PO might have been approved any number of times, it'll only return the name of the first person where there is an "APPROVE" Action Code against them.
-- see who first approved a PO select distinct pha.segment1 po , pah.action_code , pah.action_date , papf.full_name from po.po_action_history pah , po.po_headers_all pha , hr.per_all_people_f papf , (select min(object_revision_num) minrev, object_id from po.po_action_history minact where object_type_code = 'PO' and action_code = 'APPROVE' group by object_id) minbob where pha.po_header_id = pah.object_id and pah.employee_id = papf.person_id and minbob.object_id = pah.object_id and pah.object_revision_num = minbob.minrev and sysdate between papf.effective_start_date and papf.effective_end_date and pah.object_type_code = 'PO' and pha.authorization_status = 'APPROVED' and pha.creation_date > '20-AUG-2013' and pah.action_code = 'APPROVE' order by pha.segment1;
To find the approval limit for a person first find the assigned approval group for that person's position/job using
Purchasing -> Setup -> Approvals -> Approval Assignments
And then query approval groups to see the approval limit for the persons having that approval group
Purchasing -> Setup -> Approvals -> Approval Groups