I can answer some of these...
-3600mhz isn't available? Different country? I literally just bought this kit from them:
https://www.newegg.com/g-skill-32gb-288-pin-ddr4-sdram/p/N82E16820232881
-Not much point to it, it seems, unless you work in a datacenter. I'll post this quote:
"Despite the theoretical “RAM bandwidth doubling”, the only apps that will actually benefit from that are those where the processing is highly data-intensive, the rare apps with low L3 cache hit performance. Think working on huge independent data sets, a program with thight loops, so you’re constantly needing the RAM bandwidth to feed the CPU with completely new data, and the CPU spending most of it’s time asking for completely new data to process.
However, for most normal usage apps, even the latest games, the biggest benefit is getting bigger on-CPU L3 RAM caches, size if such RAM caches increase when going to a higher number of cores (those i9 CPUs don’t cost tons for no reason). Most of the time, your app’s “next bit of functionality or data” will nearly always come directly from the cache. The 1% of the time that you get a cache miss, THAT is when you’ll get twice the bandwidth, but 98% if the time, you get no benefit, because your RAM access remaining in on-CPU cache anyway, so you seem to see your overall performance go from 100% to 102%, not from 100% to 200%! So quad-channel is really a bit of a waste, for most people.
If you’re a professional working on on say meteorologic or seismologic data, go for quad-channel RAM. Otherwise, nope that “double your RAM bandwidth” won’t give you faster apps. At all. Going for more cores will."
-DDR4 3600+(OC) means '3600 or higher OverClock'. It's best to consult the motherboard manual - or even online manual - for compatible memory kits.