אע"פ שאדם שומע כל התורה כולה כל שבת בצבור חייב לקרות לעצמו בכל שבוע פרשת אותו שבוע שנים מקרא ואחד תרגום אפילו עטרות ודיבון:

Even though each person hears the Torah reading each week in the public reading, we are obligated to read each parasha twice in the hebrew and once in the Aramaic targum. Even the verse "Atarot v'divon" (Numbers 32:3).

Rashi's commentary shares the status of Targum, and those who fear Heaven will read the parashah with both Rashi's commentary AND the targum.

The first day of the week is considered 'with the congregation.'

The 'choicest' way to perform this commandment is to complete the reading before the Shabbat meal. If you missed out on the opportunity to do so, you have until Mincha. Others say until Wednesday the week afterwards; while others even say you have until Shmini Atzeret (Shmini Atzeret is Simchat Torah. So you are completing the Torah reading with the community).

You can perform shnayim mikra at the time of the public Torah reading. (And see above Siman 146)

Teachers do not need to repeat the Torah reading to themselves since they read it during the week to their students.

On festivals there is no need to perform shnayim mikra. RAMA: Similarly, there is no need to read their haftara readings (Mordechai). However, there is a prevalent custom to read haftarot on festivals. On the week of a wedding you read the regular haftara, and not 'I will surely rejoice.' (Piskei Mahar"ai)