Jaquemontii birch is much more popular than it was when I planted mine- you now see it even in commercial plantings.
Another possibility is a maple - perhaps a snakebark species with a green trunk with white markings. They don't like full sun or wind, so I'm not sure it's suitable.
Round the base of the pond I'd be putting something low and slightly creeping, so it would cover the edge of the planting pocket and look as if it had arrived by itself. Aubretia, maybe a thyme or golden marjoram, that sort of thing. In a similar position in my garden we have alpine strawberries - they did just arrive by themselves!
If you've only got a narrow bed along the fence, you won't want shrubs or vigorous perennials - they'll grow over the lawn and it'll be difficult to keep the grass tidy. Perhaps climbers or things that can be espaliered. Lonicera henryii is a lovely evergreen honeysuckle with subtle peachy flowers followed by black berries, but is very vigorous - you'll have to be careful to keep it in check. Mine has now rooted over a length of 20m, and the trunk is 6inch dia. There's another evergreen honeysuckle with much smaller leaves, and that has cascades of purple berries.
Think hard about the box. There's some pest/disease rife, and the RHS has been running trials of suitable alternatives. They suggest alternatives like the small shrubby Loniceras or Ilex crenata.