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.
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.
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.