On first glance, looks like a functional ITX build. I built mine in an NR200 with the 5600G while I waited for GPU prices to come down. I think you'll be pleasantly surprised by what you can do with just an APU.

Some things to consider with an APU-only build:

• Look into adjusting the Infinity Fabric speed. Your performance will be directly tied to it and the RAM speed. See MemTestHelper.
• Do you have case fans? Even if it's a mesh case, you'll still need to remove heat out the back or top.
• Will that cooler fit? Does the case have appropriate mounting points? Will you be able to route the hoses the way you want?
• Do you need a liquid cooler at all? The 5700G is a 65W tdp processor, so it can be cooled with a variety of coolers, like a Scythe Big Shuriken 3 or a Noctua L12S, and you can often save money by considering air cooling options (plus, no chance of leaks).