Tod, I discussed with you on PM previously. It's 5 years from date of visa issue as I understand. Apparently just show current year policy and still get 5 year stamp. It's not my stamp.
Look at the Sydney consulate website. It has all the forms and a checklist. An agency wouldn't be of much use. YOU need to get the police check, doctors certificate, bank statements, photocopy of your passport, etc. Just follow the checklist. Also see the Sydney unique O-X requirements. Money in an Australian bank or Super account will meet the requirements for a 5 year entry stamp.