Hi.For you first question, I think it is because pywikibot/version.py wants to get your version from your git repository:
See pywikibot/version.py:
try:
(tag, rev, date, hsh) = getversion_git() -> it will try to run git, which you do not have installed.
How to prevent them, I have no clue right know.Just a rough idea, if possible at all: it should be checked that you have git before invoking it or block the error message from the system.
Regarding your second point, see it as an opportunity to learn :-)