1 I'd use 'ended successfully' or something like that
2 I'd use 'high' there.
I'd use 'high' for a real improvement and 'positive' for finishing something better than expected. For instance, the recent Middle East talks ended with an agreement to meet again- that's not much, but it is a bit positive, so you could say they ended on a positive note, but high note would be too much.
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