I'm making a "banked" garden out of gabions (mesh cages) filled with concrete and brick rubble from recent build and then clay, from footing, backed against it. Part of the planting I want to do is ericaceous.

Gabions

Clay piled against gabions. Topsoil pile (far right) and smaller pile of "rubble/soil mix" to the left of it.
Imagine, if you can given the Building Site state of the photos!, that this will be a semi-circular banked "end" to the garden room. My plan was to put some additional gabions around the curve, and then fill, in front of them, with (bought-in) ericaceous soil. This will keep it's cost to a minimum. My thought was to only fill those gabions with bricks, as I presume that borken concrete would be alkaline, and hopefully bricks will be "inert"?
The rubble pile has lots of both topsoil and clay mixed in. Once we have manually taken out all the decent sized rubble for the gabions we are left with a mix of fine clay and topsoil and lots of small rubble (tennis ball sized or smaller). My thought was to spread this over the clay banks in the expectation that it will improve drainage.
Then my plan was to put back all the topsoil on top of that, together with plenty of muck. I have plenty of both, so should be able to do at least a foot of covering.
The ericaceous soil, on the semi-circular bank in front of the isolating gabions, will just be ericaceous (although I may add some peat). I plan to plant this with a bank of Azaleas - something that, ordinarily, we cannot grow here.
Behind the ericaceous bank will be the clay bank (i.e. once covered with drainage-layer and topsoil/muck), and extending higher up, and also with a winding path through it, coming "downhill", I plan to plant Inkarho Rhododendrons, that are lime-tolerant. I plan to add peat to the topsoil to make it more Rhododendron friendly, and also retain moisture in summer.
I also want to plant some Acers around the clay banks. My thought was to excavate a reasonable "pit" and fill with ericaceous soil to give them some help.
There will be a winding path from the highest point of the bank (which will be raised by about 2.5M above normal ground level). My guess is that the path should be 3' wide, my plan was to use the JCB to level a 6' wide path, buy in some decent sized "rocks" that will be about 1' high by 1' deep, line the path with that and then put my topsoil behind that. That will give me an instant 1' height start to the beds on the banks which will mean the plants have 1' less growing to do before they are useful! They need to be 6' tall along the winding path so that it is not possible to see "Into" the garden until you have come right down the path and are "in" it. I also thought that the rocks would stop the banks washing down / collapsing onto the path.
I hope I have explained that well enough? If not please ask any questions. Thanks for you help, its my most grand scheme yet! and it would obviously help if, with you help, I can get it right-first-time.
The effect I'm wanting to create is similar to the Japanese garden at Compton Acres (in Dorset):

and I also like the look of photos I've seen of the Azaleas at Isabella Plantation, Richmond Park




