New to Macs looking for fastest drives.

I am new to the Mac world and bought my first product in the form of a new Mac Studio,

I just ordered your Super Thunderbolt 3 Dock with PCIe 3.0 m.2 slot and I THINK SATA III 6GB/s SSD slot

I am still trying to find the fastest 4TB drive options for my wildlife photography/video and sublimation craft designs.

Are there capacity limitations on the ports or can I get 4TB in both the SSD and the m.2? I do have a couple 2TB Samsung m.2’s available, but not sure which SSD to get.

I am researching the issues with drive speeds being slower on Apple M1 chips than they are suppose to be and hoping it is correctable with a future firmware update or something.

I was wondering if there are any plans in the near future to make a new version upgrading to Thunderbolt 4 with PCIe4 interface speeds?