I am no expert but won't building up your backyard take more fill and may create drainage issues around your house, unless you are also planning a retaining wall?

Hi Roger, With the pleached trees, I think your underplanting amps up the tropical look especially if you go with a magnolia that have the dark green upper leave and the bronze underside. You could just go for banana or palms - personally I think you might be right about the clumping bamboo becoming a bit dense. Regarding your 400mm retaining wall - citrus are shallow rooted and tend to have a root system that goes out to their drip line. Maybe if you put it in a corner you can use the corner to espalier it in conjunction with staking it to get upper stablility but I'm not sure how it'd go with the roots - but give it a go at $30-50 depending upon size it's not an huge amount if it doesn't do well - just dig it up (just watch the thorns) and give it to a friend - check out Daileys for varieties and maybe get in touch and see what they think, they might do them on a dwarf root stock - I've found them to be helpful in the past. i'd be reluctant to underplant any kind of citrus though - as they are shallow feeders.

A pool of any sort is going to be expensive. The photos imply quite a steep slope. You either need to cut in or raise up, both of which will require elaborate and costly engineer designed retaining walls. Why bother? It's a great looking natural site that could be really enhanced with a good garden that would retain the slope and be far cheaper.

Gosh yes pebbles and pools don’t mix well. You need to keep a higher edge around pool from the surrounding ground, at least the area outside your pool fence to minimize overland water flow into pool during storms. The type of surface depends on your budget. I would keep the larger area fairly simple and dress up the smaller pool surround for feature. This work is not cheap so best getting a landscaper involved to ensure it meets your needs