HI - I would plant a ground cover plant that is in your growing zone . Maybe a wooley thyme would work or carpet roses . Anything that is close to the ground . Or some variegated or grey color plants . Or a big rock would fill the empty space . Your tree needs to be pruned a little to encourage a nice shape .

I would suggest a hardy perennial with color that compliments but does not match the roses on the opposite garden. A short to medium height salvia would be striking and be miminal upkeep in the full sun setting you appear to have. Alongside the sage put in a 2 or 3 small to medium moss rocks with sharp or angled corners and nest the salvia in its niches.

I would move that tree since it is blocking the door. Search on here they have a lot of landscape design.

Randomly move your rocks around so they're not all clustered together. Like the ground cover suggestion above. You could also shape the garden as it nears the sidewalk, echoing the curves at the top of the garden.

I would probably transplant the clump of ornamental grass. It is too tall for its location and consuming the more attractive ornamental tree. I, too, advise increasing the size of the planting bed beside your driveway, adding curves that will permit you to plant appropriate perennials as well as annuals as the season permits. The grass is a nice plant in the wrong place, I think. It will look better in a less obvious spot in your yard.