Regarding question 1 - 1/2 inch to 5/8 inch. You can use a piece of scrap as a spacer under the sheet to measure (the scrap is 1/2 or 5/8" thick).
Regarding question 2 - I am unclear what you mean by ribbed metal. That could be J metal, L metal, 90 metal, hat rack or PCI metal, tape on L...