My house is pretty simple, a stright forward roof, no hip roofs or odd ball corners. I have a 4-12 pitch, I do have one small "peak" (gabel) area above my garage but I may not even have to re-do that part it does not look bad at all. Alot of my roof wear seems due to tree damage from large trees that were around the house when I bought it- the trees have all be cut down and removed so they won't be a issue anymore. I only have about 1,200 square feet of roof. I figure I can do a small section at a time. Roofing is pretty simple it's not rocket science and the biggest cost in roofing is the labor. I also learned that some places even deliver your packages of shingles and can even roll them out to the roof on a conveyor line from the truck so I won't have to carry the bundles up the ladder by hand.
Don't do any of it unless you are gonna do ALL of it!! You have them delivered to the roof - that puts all the bundles up there so you only have to do one at a time. How old are you?? How much roof walking have you done?
I used galvanized nails on mine, but staples done properly should be just as good. Some say better, 'cause there are two holding points per fastening point.
Probably should have someone do it for you. (I've done a couple dozen roofs over the years, and at this point, probably won't mess with that again - let someone else get that hot.)