Stuck with my compositions

I need some opinion. I want to write 4 piano pieces for my final exam with around 1:30 per piece in a Brazilian style (like bossa nova and choro). So there are a lot of syncopated rhythms and extended chords. I have started listening to some Villa Lobos as well, but I have had a lot of difficulties when it comes to compose. My idea was to take the main motif from the repertoire I'm going to play and use it to compose my own work. But I'm having trouble developing this motif in a way that pleases me, and also creating a contrasting section.

I know there is one technique where you develop your motif in many ways (retrograde, inversion, interpolation, augmentation, etc.), But would it be possible to compose a piece with only these techniques?

Is there no "relaxation" moment where these techniques are not used?

Also, do you think 4-part writing study is useful for my goal?

I know it's useful in general, but is there be something that would be more important for me to practice at the moment?

I really want to do something special and good enough, but I'm still a beginner and need some advice.

1 hour ago, Jurio09 said:

I know there is one technique where you develop your motif in many ways (retrograde, inversion, interpolation, augmentation, etc.), But would it be possible to compose a piece with only these techniques?

Yes it would. Fugues usually do this, breaking down the subject into motifs for the episodes if they exist, doing all kinds of things to the subject like augmentation, diminution, inversion etc. The first movement of Beethoven's Fifth is also a good example of something written by developing a motif in all kinds of ways as just about every single note of the first movement originates from the opening motif. And the Beethoven example is also a good example of how you can get contrast from the same motif as the second theme just takes the melodic aspect of the motivic statement of the horns(which is in turn an expansion of the opening motif of G x3, Eb, F x3, D), that Bb, Eb, F, Bb, inverts it so it ascends rather than descends, and connects the notes to form a new melody from the motif.

1 hour ago, Jurio09 said:

Also, do you think 4-part writing study is useful for my goal?

It definitely could be, especially if you want to go down the route of fugue rather than something closer to the Beethoven. And if nothing else, it will mean you have more skills and can write things like string quartets and stuff better.

1 hour ago, Jurio09 said:

Is there no "relaxation" moment where these techniques are not used?

It depends. In a fugue, not really. In the Beethoven example, the second movement uses much less of the opening motif than the other movements, mostly using it in the transitions from the Ab major theme to the triumphant C major that foreshadows the Finale.

Thanks for your help!

The Choro is a most interesting form as it emerges into art music. It may be worth listening to composers beyond Villa-Lobos - Gnattali, maybe, a few pop composers too. The problem will be coming up with tunes. And it depends on how adventurous you want to be. Perhaps take a popular tune or two; work out the harmony then change the tune a little so it still fits the harmony. 

It's how I've gone about it in a couple of my pieces although they weren't for exams. I get too influenced by Brazilian composers when in that mood.

This is an interesting approach, I'll try it. I got curious, how would you do if they were for exams? It's just because these composition are meant to be played in a kind of final exam from the music school. Thank you for your comment.