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I'd remove the shrub in the corner and just mulch that spot. Replace the shrub on the far left to maintain symmetry. I'd add in some sun loving perennials like, purple coneflower, black-eyed Susan, and beebalm. That will give you lots of color. I don't use weed barrier. I use layers of cardboard. Wet each layer and then top with 4" mulch. It decomposes over a couple years, but it's enough to smother existing weeds. After planting definitely install some drip irrigation (soaker) hose and a timer. It will automatically water for you. I usually place this before I mulch. Make sure you test it and look for kinks before you cover it. I use landscape staples to keep hose in place around plants.