Grab the 3070 if the price difference is only $50. Will definitely hold up longer, imo. None of the brand are bad, but I'd say EVGA has the better CS policies and overclock pretty good.
Ryzen loves higher speeds, so I'd say go for 3600. My RAM CL is currently 18, but if you're willing to spend a little more, get CL16 RAM with 3600Mhz. Will be butter, but CL18 is more than fine, too.
This will be more than enough
If all you're doing is gaming, I'd say grab a B550 motherboard. Brand depends on your personal preference. I.E aesthetics, wi-fi needs. I've used Asus and MSI boards personally. Like the looks of the Asus boards better.
Just get something with decent airflow. Everyone loves the Meshify C. I currently have the be quiet! Silent Base 802 Airflow version
I personally like Air cooling, but AIO is more than fine. Go with the AIO since you like the look of that better. They'll both do the job just fine as the 5600x is a 65tdp part.
Yup. Corsair, Seasonic, be quiet are pretty good. If you head to Linus tech tip forums, they have tier list over there that might be helpful.
Samsung, Western Digital, Seagate, etc they're all fine NVME's and you'll be fine with either Gen3 or 4 parts.
1440p also appears to be the sweet spot for gaming right now. 4K looks to be creeping up for PC gamers. 3060Ti will be great, but as I said, for $50 I'd take the 3070 all day. I wanted the 5600x and 3070, but I built my newer rig early December, so parts were scarce. Currently using a Ryzen 7 3700x and MSI Ventus 2x OC 3060Ti. Haven't had any issues and gaming is joyus. Plan to upgrade my monitor to a 1440p soon as well, so with your current list of ideas, you'll have a ton of fun. Good luck with your building and choices.