Pics are a great help. Isn't it going to be lovely! Lots of character already as a result of all the hard work doing the terracing.
Think the gunnii in the link is gunnii divaricata - which tends to have several trunks. Ordinary gunnii tend to be single trunk, but the one in the photo may have been cut low when young, thus forcing many stems. It looks ideal in the photo - but it won't stay like that and could get jumbo big. But, as you say, you're willing to keep it in trim.
You could think about a few shrubs like mallow or buddleia, which would be quick growing and attract lots of butterflies, and insects. Buddleia 'lochinch' is a good variety which doesn't get too tall.
Somebody suggested Hazel - new one on me - looks good.
Think the gunnii in the link is gunnii divaricata - which tends to have several trunks. Ordinary gunnii tend to be single trunk, but the one in the photo may have been cut low when young, thus forcing many stems. It looks ideal in the photo - but it won't stay like that and could get jumbo big. But, as you say, you're willing to keep it in trim.
You could think about a few shrubs like mallow or buddleia, which would be quick growing and attract lots of butterflies, and insects. Buddleia 'lochinch' is a good variety which doesn't get too tall.
Somebody suggested Hazel - new one on me - looks good.