Good idea to invest some cash in the models of 3drt.com.
But I personally would import the ground as a hmp with a terrain-shader.
Otherwise the ground looks like crap - like your screen shots show it.
Biggest problem is the in the pack included blurred skymap. It simply does not fit with the level.

...btw. I must agree with blattsalat. I was a big fan of the original airfix game. Fly through children rooms, in the garden or in the kitchen - this was a cool and insane principle.
You really should come close to this principle. Make a cool airfix game or compare your work with regular air combat games - and lose.