whole plot looking north

I bet it will look wonderful :o)

Your project is interesting. Is the clematis supposed to grow up the trellis? I wouldn't do that. First I would take out absolutely everything which is now growing on the plot you want to redo. I'd consider the various aspects and make some drawings, look through magazines: the facade of the house, all the borders and the open area. For the wall of the house, I'd consider an espaliard something. Most elegant would be hydrangea petiolaris. It is slow-growing, but it's worth waiting for. And I believe that it is practical for a northern exposure. Fast-growing things are often not nearly as classy as the slow-growers. Or you could espalier a tree. A clematis up the front of the house will look messy and kind of "tied-up". If you had some kind of architechtural corner it could grow up and into, it would be better, but just flat against the house, supported by a trellis... I wouldn't.

For the border with your neighbors, I'd invest in a boxwood hedge. If you start with fairly good-sized plants, it doesn't take that long to grow into a respectable hedge. Maybe even the large-leaved box, which looks a little looser and doesn't need clipping. Yet you can keep it discreetly in shape if need be. ALL flowers look great in front of deep green box.

Naturally, you have to know if you want a low- or a high-maintenance garden. With a small space, like the one you have, don't try to include too many elements. Less is more.

We'll want to see the "before and after" pics!