Don't go to Ebay. The chances of a very unhappy ending are WAY too high. Plus, most any reputable seller of new hardware there is already selling on Amazon for less in most cases.
Buy your hardware through a reputable retailer. I can't express enough how important it is to have full warranty coverage for all hardware because these days hardware failures are all too real, and common. Just my 2cents on that because I see all the sad people here and in my shop, that didn't do that.
For what you want to do, this would probably be a very good choice. Passive fanless, so no extra noise to affect sound or audio recordings, etc. This will have no trouble with playback of 4k video or multiple monitors. The only issue might be if you need multiple HDMI or DVI outputs, or if you need Displayport or VGA, as it lacks those. Knowing what inputs your monitor or monitors have might be essential but until then this is a decent choice that definitely doesn't break the bank and is far more capable than most any integrated video.
https://www.amazon.com/dp/B072HRD3CY/?tag=pcpapi-20
As for your motherboard, you might also want to make sure that the board you get is one with excellent shielding and audio isolation, because not all of them have that. Even though I'm quite sure you are using an isolated and separate professional sound card, there are STILL audio artifacts and potential ground loops or hums possible even on a disabled onboard audio circuit that is unshielded and is not isolated. Many modern boards do have it, but not all, so I'd check. Can't hurt to have that even if you have no intention of using the onboard sound. I'm sure you're already aware, but I always like to mention it because you never know what somebody does or doesn't know.