Berlioz was much more interested in the gothic, timbre, technologies of the orchestra. On Berlioz and Paganini, see Maiko Kawabata, “The Concerto That Wasn’t: Paganini, Urhan and Harold in Italy,” Nineteenth-Century Music Review 1, no. 1 (June 2004): 67–114, https://doi.org/10.1017/S1479409800001889.
Paganini was an improviser. A lot of the good bits were probably recycled licks and phrases, with his knowledge of theory and convention filling in the gaps.
He must have known what he was doing in a formal sense.
You may recall that he heard much Italian opera when he was very young. It seems to me that Italian opera was (at least in part) his aesthetic muse. Just listen, for example, to the opening of the 2nd Concerto. It sounds like dramatic orchestral introduction to an opera. You can almost imagine a curtain opening. And when the violin comes in, it's set up like a singer with an opening aria.
In fact, I think all of his concerto sound in many ways like instrumentally inspired operatic arias, with the solo violin as a kind of incredibly superior voice.
Just a thought.
I am not aware of anything in particular that he composed for viola, although it was undoubtedly present in his few orchestral works.
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