Hey Tim,
For the first few times trying this serve I think you are picking it up pretty quickly really! I would say the main things to work on at the start and looking at yours here is just keeping going with doing a little practice each day, focusing on getting a soft contact on the ball and also trying to keep the action the same for topspin and backspin and only really change the bat angle with the wrist.
Also as your throw the ball up really bring your elbow back so you can accelerate into the serve, think about the feeling of like a small jab punch. If you can get this action with a light touch on the ball I think you will develop this very quickly. The other thing which Pär talks about a lot in the course is the relaxed grip and wrist so be sure to think about that when you do your serve practice. But keep it up it, this is a good start already!
