I have built many wheels from scratch, and revived more by replacing (just) the rims. These do not look like deep scratches, and if you ride a few hundred miles, especially in the rain, they'll be gone due to erosion from the pads. Unless there is something structural I cannot see, or if the scratches cause a brake pulsation that drives you insane, then I would leave them as-is and ride them hard.

It is good that you have the 8-speed 7403 freehub, which takes a 8-10 speed Hyperglide cassette, as opposed to the completely orphaned and impossible to find cogs for 7400 and 7402 models.

Yes, you can install new rims if the number of spokes and the ERD is the same. I'll assume that the spokes are not mangled from getting tangled up with a racoon.

I also know that Mavic rims need to be measured, as the ERD tables that I have are unreliable.