I have to patch parts of the exterior stucco where I put in new windows.
I have never done stucco before, but I figure it can't be all that
different from everything else I do with trowels.

Given that I want to be able to by supplies incrementally from Home
Depot or Lowe's, what should I look for?

Some stucco advertises that they have fiberglass in it for extra
durability. Is that something I would want?
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Uno