yes, I love using oils.
Water will mobilize oils somewhat and move them down the hair shaft. Depending on how porous your hair is, and how penetrating the oil is, some of the oil will be absorbed by your hair and act as a leave in. The less penetrating oils can tend to build up, particularly jojoba and mineral oil.
No oil is water soluble.
You can use any oil on hair. Different hair will prefer different oils, and you'll have to experiment a bit.
Those will both wash out oil very well. Oils arn't as hard to wash out as silicones.
Conditioners do contain mild surfactants and can remove some oil buildup.
Those won't remove oil any more than water will.
Yes oil will dissolve other oil, but you will still have oil in your hair. You will just be adding more oil. The thing that actually removes oil in OCM is heat, water, and friction, and that works to remove oil from hair too. Stand under a hot shower for long enough, and a lot of oil can be removed from the hair.
Oils are best put on from most penetrating to least penetrating. Saturated (solid) oils and butters are very penetrating in the hair shaft. I like these for deep oiling treatments. Monounsaturated fats like olive oil are semi penetrating. I like olive oil as a gloss. Polyunsaturated fats are not very penetrating. Mineral oil is not penetrating at all.
Hair can absorb oil, and weather and wear will remove oil, so using oil doesn't automatically mean that you will feel oily or that you'll need to use shampoo. Just don't use too much. The only time I need to remove oil is after a deep oiling treatment, even then I deliberately don't remove all the oil. In the right amounts, oils make your hair soft, satiny, and less frizzy, without feeling oily, greasy, or weighed down.
2c/3a, M, ii, porous, good elasticity, APL, silvery dark brown.
Love coconut oil, olive oil, and Everyday Shea!