1. How many steps does the guard take during his walk across the
tomb of the Unknowns and why?

21 steps. It alludes to the twenty-one gun salute, which is the
highest honor given any military or foreign dignitary.

2. How long does he hesitate after his about face to begin his
return walk and why?

21 seconds for the same reason as answer number 1

4. Does he carry his rifle on the same shoulder all the time and if not, why not?

After his march across the path, he executes an about face and moves the rifle to the outside shoulder.

There are no restrictions on guards' off-duty drinking.  They cannot disgrace the uniform {fighting} or the tomb in any way. After two years, the guard is given a wreath pin that is worn on their lapel signifying they served as guard of the tomb. There are only 400 presently worn. The guard must obey these rules for the rest of their lives or give up the wreath pin.

The shoes are specially made with very thick soles to keep the heat and cold from their feet. There are metal heel plates that extend to the top of the shoe in order to make the loud click as they come to a halt. There are no wrinkles, folds or lint on the uniform. Guards dress for duty in front of a full-length mirror.

The shoes are standard issue military dress shoes. They are built up so the sole and heel are equal in height. This allows the Sentinel to stand so that his back is straight and perpendicular to the ground. A side effect of this is that the Sentinel can "roll" on the outside of the build up as he walks down the mat. This allows him to move in a fluid fashion. If he does this correctly, his hat and bayonet will appear to not "bob" up and down with each step. It gives him a more formal and smooth look to his walk, rather than a "marching" appearance.

The soles have a steel tip on the toe and a "horseshoe" steel plate on the heel. This prevents wear on the sole and allows the Sentinel to move smoothly during his movements when he turns to face the Tomb and then back down the mat.

 There are no wrinkles, folds or lint on the uniform. Guards dress for duty in front of a full-length mirror.

Once the sentinel has completed his or her training, he or she is examined formally for proficiency in performing the duties and in knowledge of ANC. He or she must first pass a written examination of 100 questions about ANC and then be evaluated on proficiency in keeping watch at the Tomb of the Unknowns.

Upon successful completion, the soldier is awarded a temporary Tomb Guard's Badge at a ceremony presided over by the company commander. The Badge is one of the Army's higher honors and can be taken away from the soldier if he or she does not continue to maintain the highest military standards.

A Tomb guard's behavior is not so stringently regulated that he is prohibited from speaking to anyone for a full six months (someone seems to have confused the Old Guard with a monastery!), and guards may do whatever they want (including watching TV) during their off-duty hours. But since any soldier wishing to become a sentinel must undergo rigorous training, including several hours a day of marching, rifle drill and uniform preparation, and every tomb sentinel is expected to be completely versed in the history of both the tomb and of Arlington National Cemetery (including knowing how to find the graves of all the prominent person buried in the cemetery), they don't necessarily have a lot of free time to devote to recreational activities.A guard must memorize who they are and where they are interred.

Among the notables are: President Taft, Joe E. Lewis {the boxer} and Medal of Honor winner Audie Murphy, {the most decorated soldier of WWII} of Hollywood fame.

Although serving as President of the United States qualifies one to be buried at Arlington National Cemetery, only two former Presidents are interred there — William Howard Taft and John F. Kennedy

Much of the above information, courtesy of http://www.snopes.com/military/unknown.asp
 

 ETERNAL REST GRANT THEM O LORD, AND LET PERPETUAL LIGHT SHINE UPON THEM.

In 2003 as Hurricane Isabelle was approaching Washington, DC, our US Senate/House took 2 days off with anticipation of the storm. On the ABC evening news, it was reported that because of the dangers from the hurricane, the military members assigned the duty of guarding the Tomb of the Unknown Soldier were given permission to suspend the assignment. They respectfully declined the offer, "No way, Sir!" Soaked to the skin, marching in the pelting rain of a tropical storm, they said that guarding the Tomb was not just an assignment, it was the highest honor that can be afforded to a serviceperson. The tomb has been patrolled continuously,
24/7, since 1930.