@nullPointer without seeing a part’s list of the proposed future build it is very hard to answer your questions. I would suggest creating your own post for the new build because you are probably going to get more responses if you do.
Now I can answer some of your questions right now, but keep in mind I am no expert on this subject matter, and only know what I have read here on this forum or a few other websites.
from what I read you probably need a sound card that supports SR-IOV and passes through it to the virtual machine. The advantages of an SR-IOV sound card is it can work at the same time on both the host and guest. You probably would need two sets of speakers as @SonWon suggested. Most people just pass through HDMI audio feeds from their guest monitor. Yes, you will need two monitors unless you use a program called Looking Glass. But I would suggest not messing around with it yet, it is in a very early alpha state right now, so I would suggest getting two monitors if you are thinking of setting up a virtual Windows 10 or 7 machine. I also forgot the mention you probably will need to use the Threadripper platform or Intel’s current high-end desktop processors because of the limitation of available PCI-E lanes on the regular desktop processors. My new build will be based on the Threadripper Platform because of the aforementioned limitations.
Now if I haven’t scared you off, I have linked the web address for Pc Part Picker so you can post your own post and probably get more of a response to your questions. If you have any more questions, please feel free to send me a privet message, if you still don’t want to create your own post, I will try and answer your questions, if I can’t, I am willing to help you find someone who can.