These are some starter ideas to get you thinking. Let's see if we can come up with some ideas that meet your goals for the backyard. You can add anything to this idea book that you like.
Budget permitting, we could replace your rear fence (which has to be removed during the installation of the wall anyhow) with a slat fence similar to this. This lumber will last longer, and create a nice rear wall with basic lighting.
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A simple horseshoe pit like this could be nicely tied in with your planter beds.
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A pergola like this would be nice. Clean lines, and larger dimensional lumber will be easier to maintain, provide excellent shade, and be weather resistant over time. We could add some very simple lighting, and a set of outdoor speakers to make it an enjoyable space.
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This is the Allan Block classic stone. These blocks are the least expensive, and work well for walls like yours where a grade is behind it with a fence.
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Similar raised beds would be attractive, and affordable in front of the rear retaining wall, and we could incorporate seating by making a larger surround. They would form a nice border for the horseshoe pit.
Budget permitting, we could replace your rear fence (which has to be removed during the installation of the wall anyhow) with a slat fence similar to this. This lumber will last longer, and create a nice rear wall with basic lighting.
Q