I used a canvas piece my 5-year-old son had painted a landscape on. I didn't add anything to the background so I could start straight away. I tried different brush strokes. I wanted a very realistic airy cloud effect. 
I found dabbing with the brush was great to get colour onto the canvas but it was very hard to blend it out. The top right cloud of my piece was done with my fingers and a bushy brush. For the rest I followed your instructions and used the brushes you used. 
I could go in again and again on this piece. Knowing when to stop is hard. The orange piece behind the blue one is why I watched your tutorial. I just started the clouds and had no idea what I was doing. 
Thank you for your tutorial :)