1: I think this is a fine first go whit your tablet !
2: The arm are just fine, but how the feet (specialy the right one on the pic) are in angel to the ground, they are above. A breakdancer might be able to do something like this but not hold that stance.
3: Allso the splatter ore ripples in the water around the foot indicates its on the ground.
4: This is all details, when you did say its the first test of this kind.
I find it really useful to sketch by hand, scan and make the ting over digitally. Your hand has a better communication whit paper than the tablet. Due to years of experience.
Keep on, i like the feel to it and the shadow mowing at the beginning of the gif.
Peace