Are you trying to plant a perennial garden, or cover a slope in a tough groundcover? They're not completely exclusive, but a lot of the things you've said you're planting go dormant in winter and leave bare spots--the more space they cover, the larger the bare spot. Their roots will help control erosion, but won't have the same effect as a true evergreen groundcover that helps block pounding rain and runoff, or block weed growth year round. The perennials will to some extent require maintenance if not the type that spread happily without dividing. So, you'd first have to decide on your functionality and look--whether a large variety of evergreen and dormant material, or a large homogeneous evergreen cover, perhaps with a few planting pockets in convenient areas. Or, maybe I'm being a little to stiff--you could, for example, try growing just a whole bunch of stuff up there and see what happens. But, I anticipate some more prolonged maintenance requiring real interest in active gardening, if you try to use too many different species.

In order to have pavers and walk that made sense, one would need to know destinations within the yard and the uses needed by the occupants. We know neither. For the sloping border, decide which is needed: screening, or screening and shade. Plant a row of small trees or large shrubs that extend above the fence to provide screening and/or shade. The plants can touch, as in a hedge, or they can be spaced out depending on the degree of screening desired. Grow groundcover below the trees/shrubs. Could add an accent plant here or there. The turf needs to be reestablished for appearance and as a functional space for activities & pedestrian circulation.

Wow. I struggle to capture steepness in photographing my slopes, but yours looks nearly vertical. Either you're a great photographer or you do have a real challenge there. If the sage has roots that hold the soil, why not increase it asap? Start cuttings and see if what you have can be divided. Add a grass that can also be easily propagated. I think the book Gardening in a Post Wild World would be helpful to you.

Terracing is the way to get a formal look. You don’t have to use railroad ties though.But we need pics of your space and you will probably need a landscape architect.