A: maybe a year or two it is metal and will rust after time.
A: The metal is galvanized so it should last for several years even buried in the ground. I have a pile of them that have been outside for over a year and they still look the same.
A: The piece I just bought measures about 0.15" thick using Vernier calipers. That is a little over an eighth of an inch.
A: Typically it isn't something that is cut at the store. A pair of tin-snips do the job just fine.