Question about MSI GeForce RTX 4090 SUPRIM X 24G

As a rule, yes. What else have you installed?

Yes, the Suprim takes a maximum of 400 watts. Normally around 300 - 350.

Could be tight with demanding games. Depends on the rest, of course.
I recommend a power supply calculator, e.g. at be quiet.

an I9 9900K and currently still a 1080ti and 64GB Ram