Prayer

There isn’t any Sunnah prayer before Friday. After the Friday prayer, the Sunnah is to pray 4 rak’ah in the masjid or 2 rak’ah at home.

NO.

Yes, providing you don’t offer another witr

The Sunnah is to offer 11. You can add more to that. Praying less than 11 is permissible but you will lose the reward

It is forbidden to pray 3 rak’ah witr like Maghrib as the Prophet salla Allahu alaihi wa sallam forbade this. Therefore, you should offer salam with the Imam when he concludes the second rak’ah and then pray one single unit with him for witr.

It is not mandatory but it is highly recommended.

No, you should recite it after he finishes it.

As long as the time for Isha is not due, you can delay it.

It is permissible because when you only say Mu’mineen, this refers to Muslims – good and bad-.

It is permissible to pray loud of these Sunnah prayers but is it not recommended. As for “Tahiyatul-Wadhu”, I don’t know what that means.