If your Roon server is not located near your DAC, then an ethernet connected DAC will have the advantage of not requiring a separate streamer. If it is located near the DAC, then I don't see that an ethernet connected DAC has much advantage over a USB connected DAC (assuming the DAC does a good job handling the USB connection).
With modern DAC implementations, both are asynchronous interfaces, with the DAC controlling all the timing. Some DACs do a poor job of isolating the noise from the interfaces, so you have to be somewhat careful with this, but the Denafrips Terminator that you are considering has an excellent USB interface that buffers and reclocks the data.
The main thing you have to be concerned about is noise on the USB connection being introduced into the DAC. I think you'd probably be quite happy with the Nucleus (using a good linear power supply) connected directly to the Terminator with a good USB cable, but you could always add something like the SOtM tx-USBultra or Denafrips Gaia between the Nucleas and Terminator if you wanted to make sure you were getting the purest signal possible.
I haven't heard the Bricasti - it could be an excellent DAC. I have a Terminator and I'm quite impressed with it.
With modern DAC implementations, both are asynchronous interfaces, with the DAC controlling all the timing. Some DACs do a poor job of isolating the noise from the interfaces, so you have to be somewhat careful with this, but the Denafrips Terminator that you are considering has an excellent USB interface that buffers and reclocks the data.
The main thing you have to be concerned about is noise on the USB connection being introduced into the DAC. I think you'd probably be quite happy with the Nucleus (using a good linear power supply) connected directly to the Terminator with a good USB cable, but you could always add something like the SOtM tx-USBultra or Denafrips Gaia between the Nucleas and Terminator if you wanted to make sure you were getting the purest signal possible.
I haven't heard the Bricasti - it could be an excellent DAC. I have a Terminator and I'm quite impressed with it.