My experience with Tibochina is rather limited, but I'll try to help you if I can. Where I have used the plant (indoors, small mall in the Twin Cities) when it was moved, we suffered defoliation, but with a little pruning and time, it recovered just fine.

As far as tree, what are you thinking? My experience with southern CA is kinda limited, yet given what you described, I'd think something considered a patio tree would be more likely to be a better choice for you (check you local garden center if you have questions).

There aren't any real hard and fast rules as far as spacing. Or if there are, none that can't be broken (often and repeatedly), bent or otherwise mutilated in one's quest to create a fabulous garden. Given your rather limited spatial constraints, what you may be doing probably isn't what most people on these forums would recommend.

But it's your garden. Make yourself happy. It's what we do.