Can I be bold here?
You are at a great start. As you continue with oils you will learn that you approach it much differently than you would an acrylic painting. Remember a few key points when painting with oil paints.
1) Paint very thin at the start with a large brush. Probably larger than you think you need. This is to make a very loose ground work for you painting. Use this stage to decide where things are, add some values and get the general idea of the whole painting on the canvas. This will be your under painting.
2) Slowly add thicker paint and as you do use smaller brushes. With oil you will learn its much more forgiving than people realize. As long as your using thicker paint, you can cover anything already on the canvas. With that said, once you get down to your finest brushes you will be adding the thickest paint. This in when your finest of details will be put in.
3) There are a ton of mediums out there, find what works best for you and your style of painting. A great place to start is just plan ol' Linseed oil. This is what will vary the thickness of your paint.
4) Look at artwork of other artist, see their brush marks, and that will help in adding surface detail and give you an idea of how to approach your painting.
As far as this painting, I like what you had done. The blending in the clouds are great, I can see some thicker paint on the water and on the mountains giving some nice texture and depth. Keep up the work, and keep posting!