With regard to the first question: places should not automatically update to the new textures/materials. This will obviously have a negative impact on some games that rely on the current textures for some specific visual effect, which will ruin some of the old experiences. I cannot think of any plausibly good reason why Roblox should force this update on old places, especially on games that no longer get updated by the creator. Additionally, it would be nice to have the option to toggle between the new and the current materials - at least for the first few months of this update. Generally speaking, the more options that developers have, the better.
As a side note, I remember when Roblox converted the original blocky terrain to smooth terrain automatically back in 2017, which messed up many old games. In my opinion, the old games should’ve been left alone even if the deprecated old terrain could impact them. This is a bit of a different situation (given that the smooth terrain update came out in 2015, I think, and then Roblox deprecated the legacy/old terrain), but felt like it was worth mentioning because of the amount of negative feedback that that automatic update got.