See Shulchan Aruch Orach Chaim 690:14 who brings two opinions. One that simply says that we don’t make a fuss about mistakes, and a yesh omrim which limits this to mistakes which don’t change the meaning.
So it would seem that according to both opinions, a mistake in the ta’amim would not be corrected.
This question intrigued me, as in the I Shul I Daven in, they say it after Maftir.
Yes, per the Mishna Berura 288:28 one may make a Mi Sheberach for a sick person on Shabbos, so long as you say שבת היא מלזעוק ורפואה קרובה לבוא.
Although I have not been able to find a source for doing this after Shishi, I have found a interesting tidbit in Sefer Shaarei Yemei ...
I would say V'zos Habrachah. Even though it only happens once a year, I can say with a certain degree of statistical certainty that it is read so many times on that one day (in order to give everyone an aliyah) that it is the most-read Parshah by far.
While it used to be commonly assumed that they would just repeat the reading as often as necessary, evidence from the Cairo Geizah revealed they would add verses after the "main" sections to have enough room for all 7 readers. While there certainly could have been many variant practices, the evidence we have points to the following end points for ...
Regarding vav, see msh210's answer here.
Regarding lamed, Wikipedia has a nice article discussing prefixes in Hebrew. A short summary follows, but see there for all the details:
Lamed meaning 'to' normally takes a sheva, although there are exceptions for cases when the next letter of the word has a specific vowel (e.g. before a sheva the lamed instead takes ...