YES...you CAN paint Acrylics over Oils!!! I do it on almost every horse I paint. I have never had a reaction nor peeling or anything go wrong. You can also paint oils over acrylics....
NO...you do NOT have to have a colored base coat on your model. I do not use any color base coat, I paint directly on my white primer. Some artists do use an airbrushed base color though, and that is fine...but you do not have to.
NO...All oil painted pieces do not have brush strokes! Many Oil artists' horses are extremely smooth, with no brush strokes. One possibility is that you are using too much paint. I paint mine in many thin layers of color. This gives the horses coat a very deep and velvety appearance, and it lets the light into the layers so my horses just glow :)
Yes...Oils take a while to dry, usually 5 to 10 days, depending on how thick you paint each layer. Very thin layers should not take any more than 4 or 5 days, then you can continue with the next layer of color. If you are using a lot of Titanium white, it may take a bit longer.
If you have a question you would like to ask, please email me and I will try to help! I work in all mediums, so I might be able to help with most questions :)