Tired/mishmash border revamp
I first planted this border up about 5 years ago and during that time it has gone under many guises! Please excuse the belfast sink, that's for another project.
I have decided that come autumn I am need to make some changes. Basically in the hope that I can finally create a border I can be pleased with. I want to focus on getting the structure right - I think that's the mistake I've made previously and why planting never looks right. The only 2 plants that are currently in there I want to keep are the Cotinus in the right hand corner and the Cornus (C. alternifolia argentea) at the left hand side of the picture. I also want to incorporate my new Hydrangea Phantom into this border. This is a rough sketch of size. The border faces s/sw and is reasonably sunny, enough to keep the Cotinus foliage dark purple anyway. But I also get away with growing some shade loving plants - although I suspect that's more to do with me living in Scotland rather than anything else!
I am after help with siting the shrubs. Am I expecting too much to get all 3 shrubs growing happily together in this border? Or is it feasible? I have only been gardening for a short 6 years and as I've discovered my failures are visualising borders when they come to maturity. I am at the stage now I am either having to find plants new homes or bin then. The Cornus will still be moveable. I moved it there temporarily last autumn to make room for the pond but doubt the Cotinus is, since it's been there since I first planted this area out. I expect to have to move many of the perennials, especially the Kirengeshoma planted in front of the Mahonia.
Please, can someone with better vision than me help me get my shrubs sorted out once and for all. I've added a couple of more pictures for reference. I should also add I am happy to loose the Mahonia and Euonymus growing against the fence. They just don't do it for me, especially the Euonymus!
A frustrated learner gardener needs your help! Thank you.