According to Chabad custom, must one be careful not to take three steps back if the person in the back of him is still in middle of Shemonah Esrei?

Yes, as is the ruling in Shulchan Aruch, which is binding on all Jewry without exception, and thus the question itself is most puzzling. In fact, the Alter Rebbe was so particular in this matter that he writes that one who doesn’t follow it will be banished from having audiences with him. Sources : See Admur 102:5; Shut Admur 12 Takanos Tefila and Takanos Liazna

How important is it to give an exact report to the insurance company, and may one exaggerate expenses, or not report negligence, in order so the insurance covers more costs?

It is biblically forbidden to do so due to the stealing prohibition, whether the owner of the company is a Jew or Gentile. One must give an exact report to the company, and may only receive reimbursement for money that he is entitled to under the contract, based on the true events that occurred. Source : See Admur C.M. Hilchos Gezeila Ugineiva Halacha 1-4

Vayehi Noam – Shulchanaruchharav.com

Saying Vayehi Noam by Maariv of Motzei Shabbos:[1]

Whenever Pesach, or any Yom Tov, falls on a weekday the paragraph of Vayehi Noam which is normally said after Shabbos, is omitted.

Q&A

If Pesach falls on Shabbos, is Vayehi Noam recited on the Motzei Shabbos prior to it?

Yes.[2] However some Poskim[3] rule it is not recited.

^{^[1]} 295/3

^{^[2]} So is implied from Admur 295/3, and so rules: Peri Megadim 295 M”Z 2; Poskim brought in Sharreiy Teshuvah 295/2; M”B 295/3;

The Chabad Custom: Rav Yaakov Landau writes in his diary that the Rebbe Rashab would recite Vayehi Noam in such a case, and so is recorded to be the custom of the Rebbe. [Kitzur Halachos 293 footnote 9] However in the Luach Kolel Chabad they write that it should not be said. See Nitei Gavriel Pesach 1, and Otzer Minhagei Chabad Nissan.

[3] Sheialas Yaavetz 19 brought in Shaareiy Teshuvah 295/2; Kaf Hachaim 295/7; Minchas Shabbos 96/7; Luach Tuchinskiy writes that so is the custom in Eretz Yisrael; They say that it should not be said when Pesach falls on Shabbos, as Erev Pesach is considered a holiday, being that its forbidden to do work from Chatzos.