Also don't azaleas need, erm, whatsit soil? You know acid - not the hippy kind.
Techincally if it has a hedge behind it and cannot be viewed from all sides it is a border, not a bed .
Also, techincally from a (traditional) garden design ponce position you should not grow anything at the back of the border which will be taller than the bed is from front to back. Apart from a tree, obviously!
With your lovely clay soil (called Hastings Bed, btw) you need to add loads of organic material and stuff. Clay is good because it is not water permeable so holds on to more nutrients, but is a bugger to dig and gets very compacted. You can free it up by adding sand, farm yard manure (FYM) - well rotted obviously, spent mushroom compost, home made compost/leaf mold etc. I would double dig it, which (if you don't know) means to take out a trench at one end and ssave this earth. Fill trench almost to top with organic matter, fym etc, dig next trench throwing diggins over the fym and so on. Until you reach the end, then you use earth from first trench to cover fym.
For planting I would decide on your colour palette first, I like a simple one personally.
Repetition of shapes etc can help make it look less busy, so a group of dwarf larkspur near the front and some tall ones at the back.
Plant in groups of 3 or 5 for a natural looking result.
Good luck