Answer: Chinese Flame Tree fits all of your criteria and grows well in Sunset zones 8-24 so I expect it will grow well in your garden. Chinese Flame tree is a fast grower so a 5 gallon is suitable. 15 gallon will already have a well developed branch structure (less training and pruning) and a 24" box will provide shade within a year or two. Chinese Flame tree will adapt to most soils, as long as they drain well.
Best wishes with your landscape!
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