I've seen the euclidean thing, And as far as i can tell, It doesnt really support dynamic lighting.
I dont neccessarily need the engine to run in real-time, but closer to something like a beefed up blender "cycles"
As well, a huge part of this is expected to be working on the hardware side, as well as the soft side.
Based on what I can gather from your stated requirements, you'd get the most bang for your buck by just writing HLSL shaders and taking advantage of instancing.
You don't *need* an external USB device and you don't want one either! Problems:
-How fast is the communication link between a USB 3.0 device and the CPU? Very slow (relatively speaking).
-If you use specialized hardware, you put that hardware requirement on your end users. That's going to add a big barrier for entry for people who want to play your game. This brings up a question you need to answer for yourself: is this a hobby project or do you want to release this commercially? If its a hobby project to "learn", then what's the value in learning something you won't be able to use in the industry? If its a hobby project to just have fun and play around, you can do whatever you want.
-A GPU IS a super computer which does things in parallel very well. All you have to do is send it the data you want it to do operations on, send the instructions, and let 'er rip. Rendering millions of voxels with dynamic lighting would be childs play for most modern GPU's. Who needs an external USB device?! Harness the power of that GPU, it's begging you to take advantage of all of its raw processing power.