Yes, the Ryzen 7 9800 X3D requires two 8-pin power connectors.
Yes, the Ryzen 7 9800 X3D requires two 8-pin power connectors.
The 9800X3D works great with a single 8-pin CPU power connector. One cable should be more than enough for two units. I’ve used one cable with my overclocked model without any problems. It consumes about 70-110 watts when gaming hard, while the 8-pin EPS can handle well over 200 watts continuously.
No, unless you intend to attempt extreme LN2 performance tuning
Don't stress about the 2x8 pin on consumer chips—it's just a marketing trick to make the boards appear better than they really are. If you have another cable, go ahead and use it to cover the holes and stop dust accumulation. Otherwise, a single cable will suffice.