The letters "RWH&E", found at the bottom of each design, stand for the printing company that produced these stamps, namely Rawdon, Wright, Hatch and Edson. "BEP" stands for the "Bureau of Engraving and Printing". 

*The reproductions of 1875 were not issued to be used as postage, but rather as "sample" stamps. The reproductions were issued as part of a set of special printings for at least two reasons. The first was to showcase a complete set of the U.S. issues for the first World's Fair officially held in the U.S., at the Centennial International Exposition of 1876 in Philadelphia. The second was to provide stamps for collectors and others who had made numerous requests for them.

Neither of the reproductions were valid for postage since the 1847 issue was demonetized in 1851 and could not be legitimately used for postage. For this reason, an EDU for the reproductions is meaningless. They were released around March 27, 1875. 

Although two-cents paid the drop letter rate, no two-cent stamp was issued. Rates to other countries varied and were usually subject to treaty. For more on this subject see the Starnes book, listed below.

The 1947 Souvenir Sheet was designed by Robert L. Miller.

4,400,000 5¢ stamps were printed in five press runs. 688,000 stamps were destroyed when the stamps were demonetized in 1851. (Brett, see below) 

1,050,000 10¢ stamps were printed in four press runs. 159,000 stamps were destroyed when the stamps were demonetized in 1851. (Brett)

The initial work on this was done by Dr. Carroll Chase in a series of articles in the 1916 Philatelic Gazette and is considered the standard for assessing the colors of the stamp. His color designations are given here by what is thought to be year of issue (the names in parentheses are the Ridgeway color names).

1847 orange brown (auburn); bright orange brown (light auburn); dark brown (chestnut brown); black brown (dark Van Dyke brown)

1848 dark brown (chestnut brown); dark reddish brown (deep Rood's brown)

1849 reddish brown (dark russet); bright reddish brown (dark pecan brown)

1850 grayish brown (light Mars brown); dark grayish brown (Mars brown); dark olive brown (Prout's brown); orange (cinnamon rufus); brownish orange (dark cinnamon rufus)

1851 deep brownish orange (hazel); dark brownish orange (dark hazel)

Roy White discusses the colors of our fist stamp, along with wonderful and carefully reproduced examples of many, but not all, of these colors in his monumental work The Encyclopedia of the Colors of United States Postage Stamps - Volume 1. His "seal brown" stamp does appear lighter than his dark brown and chestnut brown examples, while the true seal brown is nearly black and exceptionally rare, certainly the darkest of the so-called black browns. The 5¢ stamp is sometimes listed as walnut brown, a shade not listed above, but a nice example can be found in White's Encyclopedia. Another is chocolate brown, which is another shade in the dark brown category, although perhaps a touch warmer. White again has a couple of examples that do appear to be warmer, a little more orange to the author's eye, than their dark brown brethren.

In 1986 Calvet Hahn re-examined the Chase color designations in a series of articles published in the Collector's Club Philatelist.

Websites of interest to the 1847 collector:

The Collectors Club Philatelist at www.collectorsclub.org.
The Chronicle of the U.S. Classic Postal Issues at www.uspcs.org
The New York Chapter of the U.S. Philatelic Classics Society (USPCS) at www.nystamp.org
The National Postal Museum (NPM) at: www.postalmuseum.si.edu/ (enter "1847" in "Search" and click on the arrow for links)