Is this a gaming machine? If so you should be fine with the 5600X but if you intend on doing any editing work or want to hedge against future demands you could go with the 5900X. 5600X has less cores but performance is comparable/better than the 3900X and it's like £200 cheaper than the 5900X...
I would personally always go for an air cooler over water cooling unless you plan on doing overclocking. Noctua's air coolers are highly regarded.
Looking at that build you could swap out the 1000W PSU for a 750W one as well to save money. Nvidia only recommends 750W for the 3080. Also the...
It sounds like if you want more than six cores you should get the 5900X but the best reason for getting the 5900X over the 5600X is if you need it for production stuff.
