I played the Level 1-3 (First ''bost battle'') and to be honest, it was really easy.
First be maxed out (Which Mean finish the game at least once) and then proceed to this level. First of all, don't worry if you get hit by income traffic, it doesn't count as a hit !
There's one part where you could mess up and it's when the boss is trying to hit you with his missile lock-on and you have to counter him 4 times in a row, be quick and you should be okay !
The achievement pop at the end of the level
EDIT :
If you want to see a video, you can watch this one :
Credit go to LSC MrSandMan for the Video !