I am on a small block (in Brisbane) with the house setback just 5 m from the front property boundary, and thought it would be nice to have a small, but shade-providing tree in the front garden.

I have a Harpullia Pendula in the townhouse complex I'm renting in, and it is mature (about 10m tall), but has quite a narrow trunk, and I thought it might be harmless enough to plant, say 4m, from the foundations.

Does anyone have any thoughts on this, or whether a root barrier would be required, or whether I should drop the entire idea.

Harpulia pendula is a very attractive tree. I have a couple growing down here on the Central Coast of NSW. It is hard to say just how dangerous it might be. It can depend on the nature of your foundations and the kind of soil you have. I would think that four metres away from the house is fine as long as the foundations are reasonably solid. It will be quite a long time before the Harpulia might become a problem.