I have used olive, coconut and sunflower oil. Olive is most commonly used giving a good consistency and feel. I stuck with coconut and sunflower because they didn't burn my eyes. In my opinion coconut and sunflower wash off easier.
I don't believe the choice of oil makes a difference in how it looks. It is more the ratio of pigment to oil. Start one to one or slightly less oil by volume. If you try to add more oil to have more it gets a dull appearance. Have extra lights set up to make it shine. Round up some lamps around your place. Stay away from LED and fluorescent. They are too high in blue/violet spectrum and with affect image quality if you are taking pictures or video. Use warm LED or the best is old school incandescent, also they are a healthier choice for our eyes.
I use Merhon silver powder. I know other people use other products but if you make the mixture thick enough that there is no visible skin then it should work well for you. Go ahead and paint yourself now!
This seems to be the best source of Mehron powder in the UK - with reliable stock levels and reasonable postage.
Any non toxic or edible oils will be okay and work as a vehicle with it (subject to the preference of personal taste and experiences using them) . It's only if you want it to set so you can wear it out and it not rub off onto walls, furniture and other people that you need the special mixing liquid. For WAM applications I wouldn't have though this mattered too much...