Mega1987_VerOS

I think gigabyte have the X570 Aorus Xtreme ATX board that dont have any fan on it but it was all heatsink so expect it to be heavy.

Because Intel likes to squeeze you for every dollar they can
 

Well I'm the moron who bought a 3600x ?

Moderate overclocking can make the 3600 outperform the 3600x, they're the same chip with the only exception being the clockspeed. This is what I did when purchasing Ryzen 2 years ago The 1700, 1700x, and 1800x are all 8 core models with varying clock speeds. Was able to push my 1700 to 4ghz to make it as fast as an 1800x for a decent amount cheaper. You shouldn't have to do much to match clocks on the 3600 to the 3600x

Yes. There are 20 lanes available (not counting the ones reserved for the CPU-chipset interconnect). On that board, 4 are reserved for the M.2 slot, and 16 are distributed between the two full-length PCIe slots. If only the upper one is populated, it will run at x16. If both slots are populated, they will both run at x8 each. As mentioned above though gaming performance isn't affected by PCIe 3.0 x8 vs x16.

Ryzen  has 24 pci-e lanes:
 
x16 : to graphics (depending on chipset can be split in 2x8)
x4 goes to m.2 (can also be split by MB makes in x2 + x1 + x1 or x2 + x2)
x4 goes to chipset
 
chipset is like a network switch, takes that x4 and creates multiple pci-e  2.0 lanes and other I/O lanes (which are like pci-e lanes) to which the sata and usb3 controllers and other things connect to ...
note that what you see below is in addition to a few usb 3 and sata ports already inside the processor itself
 
 

 

 
 
A 10 gbps ethernet card in theory can achieve ~ 1250 MB in either direction.
 
PCI-e v2.0 can do max 500 MB/s per lane and pci-e 3.0 can do around 970 MB/s per lane so in order to achieve that maximum speed, the card needs at least 3 pci-e v2.0 lanes or 2 pci-e v3.0 lanes.
Because there's no such thing as a pci-e 3.0 x2 slot (which would have been enough),and because the card may be installed in a pci-e v2.0 slot, they made the card with a pci-e x4 connection.
 
If you can accept the card not going over around 900-950 MB/s you can probably install it in a pci-e x1 slot on your motherboard (if the slot is designed that way.. must have the wall at the end removed)... it's perfectly legitimate to plug cards with wider edge into pci-e slots that are smaller, pci-e is designed ike that, to be moduar
 
If you have a board with B350 chipset, most iikely the second x16 slot on the board is ellectrically only pci-e v2.0 x4 lanes (2GB/s in either direction) coming from the chipset, but that's enough for your 10gbps card