In the last paragraph it describes "tobacco labels" Were the POWs getting cigarettes from home? Were POWs getting letters from home?

Yes, prisoners of war were entitled to send and receive letters (part of the 1929 Geneva Convention relative to the Treatment of Prisoners of War), and did so until the final months of the war when communications really broke down. They were also entitled to receive parcels of up to 11 pounds packed and sent by relatives, not to include books or tobacco; these were sent directly by authorised dealers with special permits. Relatives would place the order with the dealer and give them an appropriate label (the tobacco labels mentioned) to send on. For more details see the Red Cross Prisoners of War Bulletin.

At the time of this letter/stage of the war would my grandmother been able to get letters to my uncle?

In January and February 1945 camps in the east like Stalag Luft III at Sagan were evacuated ahead of the Soviet advance and the prisoners marched west. Stalag IVB, being relatively central, was not evacuated. The family website of a British prisoner there, Robert Otterson, records a letter sent home on March 17th 1945, after which "It was an anxious time as regular communications became disrupted in the chaos of those final weeks" so March may have been a little too late for a letter sent from the US to make it through.

How much do we know about Stalag 4 B?

The Wikipedia page is a reasonable starting point; it was one of the largest German camps with prisoners of many nationalities including Commonwealth prisoners transferred from Italy. Kurt Vonnegut, also captured during the Battle of the Bulge, was there for a time before being transferred to a working party in Dresden. The Pegasus Archives have some photographs.

My uncle said that while in the POW camp they were served potato skins and made soup out of them. My question is this accurate? Not necessarily the type of food but rather the poor quality of food. If so was it a result of the conditions in Germany i.e. food shortages or rather just poor treatment of POWs by the Germans?

Absolutely accurate, yes. There were food shortages in Germany, but also a deliberate decision to minimise rations. The Geneva Convention specified "The food ration of prisoners of war shall be equivalent in quantity and quality to that of the depot troops", but German command reduced food allocations such that Red Cross food parcels were all but essential for prisoners: "... the low levels of rations issued by the German authorities were the result of a formal policy decision made by the OKW, who realized early in the war that the Allies could and would provide generous supplements through the Red Cross, and saw in this an opportunity to reduce the cost of maintaining the prisoners of war (thus causing the Allies to subsidize, indirectly, the German war effort)." (Prisoners of War and the German High Command, Vasilis Vourkoutiotis.

Though not from Stalag IVB, a few of accounts from S. P. Mackenzie's The Colditz Myth give an idea of camp meals:

"Daily rations consisted of ersatz tea at dawn, thin soup akin to greasy hot water at midday, and a small issue of bread and biscuit at about five o’clock. This last meal consisted of one-fifth to one-tenth of a small rye loaf—twelve inches in diameter and two inches thick—plus three-quarters of a biscuit (‘which was the size of a large dog biscuit but tasted much worse’) per man." (at Dulag 183, a transit camp in Greece)

"We subsisted on the German rations for a non-working civilian: a cup of Ersatz coffee, made from acorns, in the morning, a bowl of soup, usually Sauerkraut, with a few potatoes at mid-day, and one fifth of a loaf of black bread with a pat of margarine and a small piece of sausage or cheese in the evening" (early days at Stalag Luft I)

"By the end of 1944 at Oflag 79 there were no Red Cross parcels and daily rations consisted of little more than a cup of acorn coffee, two thin slices of black bread, two small boiled potatoes, and a bowl of thin soup."