First time PC build, Cooling question

[FeralSand]

Budget (including currency): 

Country: Ireland

Games, programs or workloads that it will be used for: DaVinci Resolve, Affinity and  Gaming (cyberpunk, fallout)

Other details (existing parts lists, whether any peripherals are needed, what you're upgrading from, when you're going to buy, what resolution and refresh rate you want to play at, etc): 

GPU : Zotac RTX 3090
CPU : Ryzen 9 3950X
CPU Cooler: Noctua NH-D15 Chromax.Black
Ram : Corsair Vengeance LPX DDR4 2x 32GB
Case : Corsair 4000D ( was aiming to get the airflow version but due to availability it  wasn't an option for me in Ireland. Although i do plan to buy the airflow front panel when it becomes available )Motherboard : Gigabyte B550 Vision D
PSU is still to be purchased Im considering getting a Corsair RM850x

Hey I'm a new member here and this is my first time posting. (so if this is in the wrong place, my apologies.)

My question is simply how many fans and what size fans should I be putting in this case and I would be grateful for suggestions on particular fans.

I watched a video by OC3D TV where they found that adding an additional fan to the front of this case had a negative impact on the temperature of the GPU. Which seems to me to be counterintuitive. 
Source video : https://www.youtube.com/watch?v=MTmp2cEkEpg

Thanks in advance , Feral

[1982 Original]

2 hours ago, FeralSand said:

Budget (including currency): 

Country: Ireland

Games, programs or workloads that it will be used for: DaVinci Resolve, Affinity and  Gaming (cyberpunk, fallout)

Other details (existing parts lists, whether any peripherals are needed, what you're upgrading from, when you're going to buy, what resolution and refresh rate you want to play at, etc): 

GPU : Zotac RTX 3090
CPU : Ryzen 9 3950X
CPU Cooler: Noctua NH-D15 Chromax.Black
Ram : Corsair Vengeance LPX DDR4 2x 32GB
Case : Corsair 4000D ( was aiming to get the airflow version but due to availability it  wasn't an option for me in Ireland. Although i do plan to buy the airflow front panel when it becomes available )Motherboard : Gigabyte B550 Vision D
PSU is still to be purchased Im considering getting a Corsair RM850x

Hey I'm a new member here and this is my first time posting. (so if this is in the wrong place, my apologies.)

My question is simply how many fans and what size fans should I be putting in this case and I would be grateful for suggestions on particular fans.

I watched a video by OC3D TV where they found that adding an additional fan to the front of this case had a negative impact on the temperature of the GPU. Which seems to me to be counterintuitive. 
Source video : https://www.youtube.com/watch?v=MTmp2cEkEpg

Thanks in advance , Feral

Since you picked out a Noctua Chromax cooler, I would buy matching Noctua fans. I would do 3 front 120mm, 1 rear 120mm, 1 top 120mm. 
 

The other option is to switch to a Be Quiet air cooler and go with all Be Quiet case fans. 
 

Third option: Be Quiet Pure Loop AIO top mounted as exhaust, 3 front 120mm Be Quiet fans as intake.