What should the chazan do if he cannot take three steps back?

After the chazan finishes his quiet Shemoneh Esrei, he must take three steps back. However, he does not have to take three steps back at the completion of Chazoras Hashatz. The three steps back he takes at the end of the final Kaddish suffice for Chazoras Hashatz. Although many passages are recited between Chazoras Hashatz and the final Kaddish, they do not constitute a hefsek. The chazan should be careful to refrain from idle chatter during this period. If there is someone davening directly behind the chazan when he completes his quiet Shemoneh Esrei, he should not step back directly, but towards one side. If there are people davening behind him in all directions, he should start Chazoras Hashatz without stepping back. Some say he should move his feet slightly from their place before starting Chazoras Hashatz. 

סי' קכ"ג ס"ה ס"ק י"ח ביאורים ומוספים דרשו 20

Why did Chazal institute Chazoras Hashatz?

There are two reasons why Chazal instituted Chazoras Hashatz: 1) Through this repetition, people who do not know how to daven are able to listen to the chazan and be yotzei their obligation. Only those who are unable to daven themselves can be yotzei with the chazan, and at least ten people must be in shul for this to happen. People who are being yotzei through the chazan must be able to understand Lashon Hakodesh, must listen to the chazan the whole time, and may not interrupt even to answer devarim shebekedusha. 2) A second reason for Chazoras Hashatz is to allow people to say Kedushah b’tzibur. In a situation where a person is unsure whether he was yotzei his obligation of Shemoneh Esrei, he can serve as chazan for Chazoras Hashatz. This will cover any possible obligation he may have.

סי' קכ"ד ס"ק א'-ג' ביאורים ומוספים דרשו 1

Why do some shuls daven a shortened Mincha?

L’chatchila, the chazan must daven a quiet Shemoneh Esrei before he says Chazoras Hashatz to make sure that he is fluent in the tefillah before the repetition. Nonetheless, if he arrives late and must serve as chazan (e.g. he is an avel or he is the only person that can be the chazan), he should just say Chazoras Hashatz and he will be yotzei his personal obligation as well as the obligation of Chazoras Hashatz. If it is close to zman tefillah and there is not enough time for both the quiet Shemoneh Esrei and Chazoras Hashatz, the chazan should recite the first three brochos – including Kedushah – aloud, while the tzibur davens along with him. After Hakel Hakodosh, everyone continues the Shemoneh Esrei quietly. Some congregations choose this option l’chatchilah for Mincha. This is known as the “short Mincha”. The poskim explain this practice as follows: Chazoras Hashatz was originally instituted for congregations which had members who could not daven themselves. Therefore, in batei medrash where all the members were always well educated, Chazoros Hashatz was never instituted for Mincha. 

ס"ב ס"ק ד'-ט' ביאורים ומוספים דרשו 13

• If a person completes Shemoneh Esrei before the chazan, he may not turn around and face the members of the tzibur who are still davening.

• A person should take the first step back with his left foot.

• There are two methods mentioned in the poskim for taking the three steps back: 1) One should begin by taking a small step back with his left foot. He should then take a larger step back with his right foot. Finally, he should move his left foot back to meet his right foot. 2) One should take his first step back with his left foot. Then he should step back with his right foot to meet the left foot. This process is then repeated twice, for a total of three times.

• Is it permissible to learn during Chazoras Hashatz?

• What should the chazan do if he suspects that there may not be ten people listening to Chazoras Hashatz?

• Is it necessary to wait for the Rov before beginning Chazoras Hashatz?