PCIe x4 clarification

You can put the tb card in any slot you want There is no tb port on the back of your mobo The back has dp, hdmi, usb , ethernet

If you have a board that does not do CrossfireSLI, then sticking a card into another slot will have no bearing on the first You could also get an enthusiast

can you run ddr4 in a ddr5 slot Physically yes, the slot connector for an x4 is generally smaller and PCIe is designed that smaller cards can occupy larger slots if needed

candy village slot png Making sure Graphics Card is running at pcie x16 speeds in bios & Windows