I think it's great that you have decided to enter the
GD.
However, since you asked for C&C, here is my advice:
Start from the bottom up, and absolutely master basic techniques, like highlighting, shading and freehand, before attempting a whole diorama.
The model shown here is needing some tlc - he needs to have much sharper highlights, much better defined details, and much thinner paint.
The best painters in the world used THIN paint, lots of layers, and slowly build up the colours. While I like the fact that you want to enter, there is a long way to go - remember you are up against the best in the world.
