No law passed by Congress required military service from slaves. Only white male citizens were required to serve.

1. Did they get the same food as the white soldiers got?
Good question. "Body servants" or slaves belonging to Confederate officers and men shared rations with their owners. When the Confederate government cut rations in 1864, Confederates write about having to send their slaves home.
2. did they get paid the same as the white men?
In order to be paid, a man had to be enrolled. Until 1865, slaves could not be enrolled in a infantry, engineer, cavalry or artillery unit. There are payrolls for state companies early in 1861 that show officers receiving pay for servants. One officer had an Irish boy as a servant. In most cases slaves were hired to the government for labor projects, so the owner was paid for services of his slaves.
3. What did the white soldiers think of them?
Depended on who you asked. Best source for that question would be the petitions and letters printed in Richmond newspapers, late 1864 and early 1865. Members of the Army of Northern Virginia were aware that Congress was debating the use of slaves as soldiers, and wrote to submit their opinions. These can be found in Robert F Durden's book, The Gray and the Black: The Confederate Debate Over Emancipation, available in paperback. Many petitions were favorable, Confederates saying that they would be willing to serve with black soldiers in the ranks and urging Congress to pass the law.
http://www.amazon.ca/The-Gray-Black-Confederate-Emancipation/dp/0807125571