Вчера, Жанна покупала 2 сумки. - yesterday, Zhanna was shopping for 2 bags. (But even though покупать means buy, it doesn't emphasize that she successfully bought it...Right? Even though the word does mean buy..)
Вчера_ Жанна купила 2 сумки. - yesterday, Zhanna bought two bags. This sentence is very strange, although you are right.

Cегодня Андрей пробежал марафон. - Today Andrei finished running a marathon.

Посмотрим фильм с тобой. - We'll watch the entire movie with you.
Будем смотреть фильм с тобой поздно. - We'll watch the movie for a while later.
Yes, you are right.