Hi Ernie and welcome to the forum.
Although I do agree with ddawg, we work for pennies when we do our own roofing, I will be doing some this summer myself. But my roof is simple and I own the staging, ladders, and nail guns (plus I'm retired) so it keeps me busy.
As you said, the key is doing it safely. A safety harness would be a first step with proper anchors, but always have someone with you to get you down as you can only hang from those harnesses for a short period. I think 20 minutes and you die from the harness.
Second step would be to see what is needed for the rest of the house. Options are scaffolding, ladder jacks, powered lifts, or your own wood staging (be careful).
Another question to resolve is, how will you get the shingles up there and of course how will you remove the old ones. Just dumping them off of the side can damage the house, windows, and shrubs. Plus it is a lot of wheel barrow work.
How many squares, Ice and water shield, flashing, new boots for vents, and any soft spots in the roof. Do you have a ridge vent and or will you be adding one?
Most important, have you ever done any roofing and do you have help. Mother nature rarely gives you a month to complete a roof.