So the most important thing is obviously that you like the setup.
I really like rocks, a lot. So I wouldn't hesitate to do something with just stone. If you wanted to go that route I would add more stone then just the one. If that stone is your focal point you should add at least 2 other smaller stones around the base. Since this is for shrimp you will want to make sure your stone is not reactive (such as seiryu stone). If this is a stone only scape I would bank the soil in one of the back corners and plant your stones into the substrate a bit so they appear to be forming out of the ground as it were.
If you have smaller pieces of wood you could incorporate that into a stone scape as well. Or you could go back to the other wood piece and just trim the branches touching the glass after you get it in an orientation you like. /shrug
DHG can be kept alive in a low tech tank but it requires decent light (no idea what your light output is in this tank) and it will never carpet like a high tech tank. But it will form little clumps which may be something you like.
In a shrimp tank I also would consider using a sand cap over active substrate just for aesthetics, but that's a personal preference so your mileage will vary.