All the above are viable options. You can overclock your CPU, RAM and graphics card if need be (As long as your motherboard supports it).
Your processor supports dual channel, which means you might be better off with only two sticks of RAM, but it might not make a big difference in real world performance.
Honestly, I would spend your budget on the best monitor you can get, preferably a 1440p monitor. 1440p or 2K is the middle ground to 1080p and 4K, with better visuals than 1080p, and less performance degradation seen in 4K. Also, the RTX 2080 is an extremely powerful card, meaning, your processor is definitely bottlenecking games before it is, and upgrading to 1440p will not only help transfer the load to the graphics card, but...