You can use different paper surfaces for different looks, such as E or pearl will give you a pastel look depending on how hard you buff out the paint. Glossy fiber will give you a faded out color look that you can build upon once it dries. Matt fiber has the most vibrant color and eaisest to use.
As far as paint, you can use Marshalls or any transparent, semi-transparent oil paint found in art supply store, color charts tell the opacity you can find almost any color that is trans. I started with marshalls and have for the most replaced with artists oils, Gamblin, Old Holland, Hollbein, ect. They also have more colors and are cheaper in the long run. I do like Marshalls Sky Blue though. Marshalls makes a PM solution that primes the print, makes the color flow, you rub it into the print with a cotton ball and then buff it out, then apply color. Also use it to thin out oil paint. I find this way too expensive and make my own using 1/3 artists turpentine, 2/3 Safflower oil. You can get both at any art supply like Utrecht Paint or Pearl Paint. Marlene is used to clean paint off areas you don't want any on. Another way too expensive item, $10 for 4oz bottle. I make my own using Sunnyside brand Carbosol found in hardware store about $8 for a quart.
http://www.sunnysidecorp.com/clean_grease_stains.htm.
The chemical is Trichloroethylene and is found in other products such as some disc brake cleaners found at auto supply if you can't find Carbosol.
Apply paint with cotton balls or swabs and lightly buff to desired finish. Take toothpicks and wooden scewers and wrap them with small strands of cotton. Roll em up with your fingers till they look like swabs. Apply paint and then use clean ones to rub out.
As for pencils, I find Prismacolor pencils work best of all and like someone posted you can dip them in the PM to soften a little. Apply then lightly rub with cotton. I use for details and are my favorite medium with photos.
Life expectancy, I don't know,but oil paint been around hundreds of years along with Safflower oil which was and is used to make white as it doesn't yellow like linseed oil can.
Correcting mistakes depend on the paper you use. RC pearl can be cleaned off with PM or Marlene, Glossy Fiber almost the same, matt fiber depends on the color and how much pm it was primed with, use Marlene, although I find reds very hard to get completly out. I never had much luck with using an eraser. I really enjoy hand coloring and find it a great break from computers.