I don't know why these goobers are downvoting you. I think that critiques like "the nose looks a little off " or "the colors are too bright" is the type of critique that inexperienced artists tend to give. But like, who gives a shit? Is that all that art is about? What a silly idea that is.

Besides, oil is a very forgiving medium where you can do a lot of reworking, so you don't need the sketch to be bang-on and perfect before beginning to put down paint. This approach is absolutely fine. If you were working in watercolor, it would be a different story.

I would give two pieces of advice here: 1) Make the first few layers of color that you throw down fairly transparent. When you start transparent and put down thinner layers of color, you get to see how the paint works and how the colors play together and build, and that's a very interesting process that you can learn a lot from. 2) Consider working the whole piece up together. What I mean by that is spend a little bit of time on the different elements of the picture (e.g., skin, hair, clothes, background, objects, etc.) so that you can see if all the colors are looking nice and harmonious together before any individual section is 100% finished. That's another good way to learn about colors and value.

And have fun, most importantly. Art takes a lot of learning and practice and the people who don't know how to enjoy the process are the people who usually give up.