Hi!
There are a few things that you would need to know and are important (been doing oils on minis for a good while...). Some colors dry faster than others. The browns do dry fast (within a few hours to a day), followed closely by black. Pure white is a slow dryer and red is the worst (a few times it did took over a week for the red to dry out! Did not used a dry cabinet as mentioned above, would be very worth it to have one!). The other colors are in between, only experience will tell you. I do recommand the red and yellow cadmium based color, they are good and strong colors, sadly not cheap thought.
Covering power is a little different from one color to the next, those that cover well are browns, black and cadmium red. White and yellow can cover well if almost not diluted. Some colors are more transparent than others, check the color chart of the company from which you will buy or, if in a artist store, ask a clerk in the oil paint section.
Also, clean well the cap before putting it back on. It will save you on trying to take off the cap without overtwisting the tube (there is real danger of breaking the tube and having a major paint leak). And if for a reason you lose the cap, it is not much of a problem, Just squirt some of the paste out of the tube and let it dry just ouside the tube exit (can flatten it a little), it will make a good air barrier, just cut it off when you need the color again. A tube can last for years without wasting.
The oil tubes are a bit sensible to temperature change, do not let them get too cold nor too hot, as the oil will try to go out of the tube and can break the cap or pierce the tube itself at the base (by overpressure). Up to now I have only lost one tube of color that fully hardened beyond hope (a sky blue color, could not find out why this one and none of the others...)
My basic color choices: ivory black, titanium white, 3 browns (burnt sienna, natural raw umber and ochre), a good red (cadmium based and costly), 2 blues (prussian blue and ultramarine blue), a green (emerald green), a good strong yellow (cadmium based and also costly), others as fancied or needed. The grey choice is good, because it is hard at first to get the same grey mixing recipe of black and white. Most oil paints are made up from pure pigments, i.e. one pure color so there is no surprise as when you mix a brown and a white, it will be a real light brown. (Not the case with acrylics where I once ended up with a pinkish beige! Arrrgh!). A color wheel for color mixing is sometime useful, but not absolutely needed.
Hope this help!