You're WELL above the recommended requirements for Fortnite
That said, most running it seem to be using 16GB RAM. Try playing with MSI Afterburner on with CPU, GPU and RAM usage and temps set to show onscreen while playing. If your RAM is being used entirely, try adding 8 GB more. It would be your cheapest upgrade and might help. Just make sure you try to find identical speed and timings on the RAM, as the PC will default to whichever is the slowest.
If you're not sure what your RAM speed and timings are, HWiNFO64 is a free tool that will show such specs.
This vid shows what I'm talking about. He has the same spec as you, but you can see his RAM is maxed, which means there's not a sufficient amount in reserve for the OS.
There is no such thing as "bottlenecking"
If, by that, you mean that upgrading a cpu or graphics card can
somehow lower your performance or FPS.
A better term might be limiting factor.
Kind of splitting hairs to be honest, bottleneck, limiting factor, potato potahto really.
You shouldn't NEED to build a new PC to hit 144 FPS though. This article makes that clear, because you obviously have better spec than is mentioned in it.
Find out how to build a cheap PC and run Fortnite with 144 FPS on 1080p monitor. What GPU and CPU make the most sense in order to play smoothly.
If the RAM doesn't yield 144 FPS, it could be something else, like your PSU, or even net connection. It's a good idea to have at least a 600w PSU for a GTX 1080. Nvidia suggests more like 520, but unless it's a very long life PSU, it's good to add as much as 100w to that.
List your ENTIRE spec, again, HWiNFO64 will help with that.
The RAM, if maxed however, could be causing those pauses, and also severely limiting FPS in doing so, because it might mean your GPU is waiting for the CPU to send it rendering data. Rendering data is calculated by the CPU, and cached by the RAM while it's doing so. If the RAM gets maxed, that could mean your CPU has to send smaller chunks of rendering data than it normally would, which is like a semi truck chugging slowly uphill because it's overloaded.