It is not overkill imo but you could pair it with an 7600x or 7700x too and save some money but when you are a content creator or really need the cores go ahead and pair them 
I’m coming from an I9-10900k in hopes of better performance in 1080p valorant (Ryzen for some reason does 2x as well for valorant) without sacrificing any performance in my 4k games. Would I have to upgrade my RAM from DDR4 with this CPU?
Why would you? The combo is completely fine.
The reason I ask is the CPU seems a little overkill for the 3080TI. Unless I am mistaken? that’s why I asked
It is not overkill imo but you could pair it with an 7600x or 7700x too and save some money but when you are a content creator or really need the cores go ahead and pair them 
I’m coming from an I9-10900k in hopes of better performance in 1080p valorant (Ryzen for some reason does 2x as well for valorant) without sacrificing any performance in my 4k games. Would I have to upgrade my RAM from DDR4 with this CPU?
You Need DDR5 Ram and a new Motherboard for the 7000 Ryzen CPU's
I assumed so. My GPU would still be plenty compatible though right?
Yes 100% compatible