SAP Security questions

Dear Experts,

Please help with following SAP Security questions

1. What is the difference between ST01 and STAUTHTRACE tcode and why STAUTHTRCE in place?
2. I have broken the relationship between master role and derived role and how do i rest it back
3. What are the authorization and tcode we should give to auditors
4. What are the critical authorization objects we should not give it to users in prd system
5. What is the use of SE54 tcode ?

Regards,

RK