Excellent dio, with tons of potential. The good thing about this dio is that when you start to learn more techniques, you can always come back and apply them to this dio!
Some things to consider that havnt been already said (mostly)
- the ground is dirt/mud, so the wheels of the PaK as well as the boots of the soldiers would be muddy. Once you start to learn the drybrushing technique, you can brush on some earth colors onto the boots and wheels.
- invest in an exacto knife and some high grit sand paper. Whenever you detach a part from the sprue, cut and/or sand off the knub left on the part. Also, sand away the molding seems on each part. They are the thin lines that run along the parts. Figures have these as well, so don't forget those.
Drybrushing would be a good technique to start practicing with, as it will immediatly enhance your modeling efforts. There are many tutorials out there, including these forums.
Get yourself an old kit to practice on, thats what I did. Preferably a cheap one with lots of figures.
Good work overall, this is a good looking dio as-is, but like i said once you start to master more advanced techniques you can always add more to this one!