A few questions on rigidity

Hey guys. I've been doing some googling but I'm still not sure on a few things so I wanted to ask here.

I've seen people say stuff like for double the size you need 4x the rigidity. It makes sense as bigger is more flex, but it got me thinking of the different factors of rigidity.

I was watching a video of a guy who upgraded his CNC for guitar building, and hes saying how its so much more rigid than his masouter pro was. But both machines use 4 v wheels per gantry.

How important is having more v wheels for rigidity (4 vs 8)? My thought is maybe the more wheels matters more when doing harder materials like aluminum? My primary goal is guitars but every now and then I think of something where I'd liek the ability to do aluminum plate.

Does larger wheel spacing effect rigidity? Some plates are bigger with larger wheel spacing.

When needing more rigidity due to being larger, does gantry wheel number or size effect this, or is it just strictly having stronger frame that the cart goes on?

On linnear rails vs v wheels, would rail rusting be a risk in very humid environments? I put some tools in my garage for storage in the winter and they definitely started rusting. summer should be a lot worse. I like the concept of v wheels and aluminum rails not having any risk of rust. Although then my lead screw could still rust so if oiling and rust upkeep is an issue I likely want to just use belts?

Bonus question I think I know the answer to, for a rectangular build, is it better to haev the X or Y axis be the long one? My thought is X as it has both side rails so it should be more rigid.

Thanks!

Heres the video I referenced for context