hello
I dont usually paint in oils, I use acrylic mostly but from what i remember you shouldnt be using water to mix oil paints, oil and water dont mix. you can get oils at the art store for mixing and cleaning your brushes, I think the most popular one is linseed oil - i'm not sure if you could use the food grade linseed (flax) oil, i'm sure it wouldnt make much of a difference. dont be afraid to have the paint fairly thick on the canvas, thats why a lot of people like oil paint, because of its thick texture. its a little different to work with than watercolour paint. It should mix on a plastic tray for you but i sometimes use one of those pads of paper in the shape of a palette (dont know if you know what i'm talking about!! you can get them in most art stores where i am), when you're finished you just throw the paper away.
Good luck, dont forget to post pictures of your work when you get going!!
M