I don't do any NIC passthrough since 2x1Gb is plenty for 4 machines and some dockers to share. Since mine is mostly setup for a gaming machine, I rarely saturate the network. I haven't measured load yet- but can tell you that I can max all cores and GPUs without hitting my 1000w ceiling. Heat isn't too terrible and the machine is in the same room as the 4 gamers playing. It does make some noise at full load but hardly more than my previous single gamer setup. The heat is noticeable after a while and we may kick on the AC that blows from the ceiling to keep us cool, but my rig never thermal throttles- it's temps stay in 55C area on CPU and 75Cish on GPU for max.
Sound issues just required me to run the msi fix and use the hdmi sound from each card. I have no sound issues and don't pass the sound card to anything. I also don't use any of the on board USB and got a card with 4 controllers to pass one to each system- saves me a ton of headaches with peripherals.
I agree with bastl- threadripper is a better way to go since it has so many PCIE lanes and cores available. Unraid does need some CPU power for itself and I have found that leaving 2 cores/ 4 smt available for it is the best plan for it to breathe freely. Plus- as he indicated- if you want to BLEED go CUTTING EDGE. It will definitely hurt until it heals with patches and updates.