Any oil paint will work although I generally use Marshall's. The Marshall oils are nice because they are transparent. However, that has more to do with the pigment than the brand. As you get closer to titanium white, the colors generally become more opaque. Darker colors like violet are going to be the most transparent.
The PM solution is essentially linseed oil and turpentine (or a similar solvent). I spend most of my time removing the color and use the extender on a toothpick wrapped lightly in cotton. For absolutely blank white areas I might use Marlene similarly to remove all the color. Smear the color on and take it off carefully, then add details with the oil pencils is basically my technique. Pencils other than Marshall's (e.g., Prismacolor, etc.,) will also work. Don't be afraid to apply a lot of color or have it bleed a bit. I think the key to hand-coloring is the skill in removing the oils. It's a nice way to spend a rainy afternoon. And good therapy...
Others have mentioned the toothpicks, cotton balls, blue tape, etc., and I use those too. I generally print a little flat and then boost the contrast when tinting. The Navy Blue and Cobalt Violet pencils are great for that. Just a little outline along a contour with those colors can make an image pop. It's also important to remove all color from specular highlight areas in the print. Otherwise it takes on a weird, unnatural pastel tone. There are also lots of different colors in what might at first seem to be a single hue. For example, when painting grass I use reds, violets, blues and yellow pencils as well as the green variety to make the area look more realistic.
My favorite paper was Ektalure G-surface, now long discontinued. A very close second was the original Foma 532 Chamois but that paper has changed. I think the newer version (532-II IIRC) would still probably be my favorite of the remaining suitably textured papers for hand-coloring.
If you ever get a chance to do a hand-coloring workshop with Elizabeth Opalenik, take it. You'll learn a lot by just watching her. I've taken two workshops from her as well as other popular photographers who hand-color and I must say I learned everything from Elizabeth combined with a lot of practice and patience. I was also fortunate to live in the same town as Rita Dibert long ago and saw her work all the time in local exhibits. I'm sure that also impacted my hand-coloring technique.
A couple examples are below. Both are around 11" in one dimension. There are several other examples in my APUG gallery.
"Polyphemus"
"Noam Stompsky" (of the Killamazoo Derby Darlins)