Neglected side garden ideas (Hunter Valley, NSW)

So we have neglected the side of the house for too long, and it’s gotten to quite the state, overgrown with weeds and who knows what else. The gap between the water tank and the fence means that we can’t take the mower through without folding it up and lifting it sideways, or taking it through the house (along the carpeted areas) There is a retaining wall about 600mm high below the fence the juts out about 200mm. Original idea was some roses there.

Problem is it only gets an hour or so of sun each day, part of it gets absolutely none and the hot water system is there, as well as the water tank overflow so it’s often quite moist underfoot. The soil is a heavy clay that won’t drain well, most of the water runs off into the drains.

What plants would be decent here, or are we better off sealing the ground and running pots instead?