It absolutely is but be aware that some cables don't support the Viper 8khz due to cable length/shielding.2: Is it worth the trouble putting a Paracord on the Razer 8K?
I bought a cable from paracablemods 2.2m (that I used for another mouse) after pin swapping the JST socket to match the Viper 8khz layout I noticed that the leds on the pcb lit up but it didn't work, asked support on Discord what could be the issue and I was told that the maximum length that they use for the Viper 8khz is 1.5 meters.
I'm currently using the Xm1r cable for my Viper 8khz with no issues or polling rate inconsistencies, tested with mouserate_x86 and mousetester 1.5.3(couldn't find the exact length of the Flexcord 2.0, it is in the 1.8/1.9m range depending on the source that I use [EGG, Caseking, Rtings,...])
It depends on what you need, Tiger Arc 1 are good if you want control, Tiger 2 are faster, Corepads are somewhat inbetween Tiger 1 and Tiger 2, Tiger Ice are the smoothest and the ones I prefer.3: Is it worth the trouble putting ( tiger arc1) skates on it?
I noticed that you plan to get another PCIe to USB card, personally I'd buy it as a last resort if all combinations of USB ports fail the USB lottery or you suffer from DPC latency issues.
Don't be scared to use onboard USB 3.0 pins that go straight to your PC case, I noticed that having the USB controller isolated from the rest of the I/O (or even DAC-UP USB for some Gigabyte boards with it's own isolated USB power design) can help.
8000hz is very buggy with Apex, I use 4000hz with 1600DPI (and 0.7sens), I can't loot with 3200dpi and 400 dpi makes it difficult to armorswap fast mid fight, looting with 1600dpi was weird at first but I got used to it since windows sens = looting sens.