both cpu NF-A15 PWM's plugged directly to MOBO's CPU_FAN via Y cable and rest of the fans plugged to HUB's 4 pin, is this the way to go?
It doesn't matter at all, you don't even have to use the case hub if you have enough plugs on your motherboard. Most high-end boards have lot of PWM headers like (CPU, CPU OPT(ional), Case 1, Case 2, PUMP, etc..) you can use directly or any combination with hubs. But your suggestion is pretty good as it would let you control the fans that should spin the same (like all intake) with single header.
I usually do all intake fans (3x) on one header (through hub or splitter), rear(1x) exhaust separately (since I want the exhaust to ramp up more than I want intake due to ratio) and CPU separately.
Regarding the CPU's fans, I highly suggest not to use two fans on thin heatsinks like U14s. I've recently read why it works so poorly (I tried it myself for two hours before I put it away). There is very little pressure needed to pass through this heatsink (unlike D15 or U14a) so the second fan will end up pulling the pushing fan a lot creating that annoying oscillating sound. Multiple fans in row don't improve airflow, just the pressure so they don't really make sense here (and the pressure starts to improve at higher RPMs, so also not situation with A15s).
(Apparently this can be alleviated by having the pushing (first fan) rotate lot less (lets say -200 RPM compared to pull) to avoid this issue. You would then have to connect the fans to CPU and CPU OPT header to control them separately.
But ultimately this is not necessary for the fact the rear exhaust fan is already doing enough pull. )I know a lot of youtubers added that second fan in their videos but.. I doubt they did any test other than because it looks better and they thought it might work better in theory.
It will absolutely fit though, Meshify S2 has 185 mm CPU cooler clearance. Every case that can fit 140mm fan above rear IO has massive space for the cooler :- ).
There's anyone that updated the BIOS of an Asus Rog Strix X570-E Gaming to the latest one (1407)?
I'm always a bit scared when updating the bios.. I noticed that on my board there is a quite old 1005 bios.
Nothing to worry about, you can always use USB flashback to bring back earlier version automatically if something happens during update process. But this bios came out month ago, it should be pretty safe.
I would try it as well, but the 3950X is with our modeler in remote quarantine and she's not a PC girl so that will have to wait :- ).
Also... if you don't have any issues.. you technically never have to upgrade bios. At some point, chipset drivers might necessitate that but the current ones don't.