Can skyscrapers grow from 5×5 lots on residential or commercial zones?
Is there any mod that can build tall skyscrapers on 4×4 or 5×5 lots?
Or can enhance textures?
Can skyscrapers grow in high density industry zones?
I realized that my comment was more of an answer, even though my memory is vague (It's been years since I've played SC4, and I don't currently have a copy.)
I seem to remember there being both 5x5 and 4x4 skyscrapers, but IIRC, the 4x4 were much more common. I do remember that skyscrapers required a huge amount of demand, so that it wasn't easy to get them to spawn. If you're having difficulty, it's probably a demand issue rather than a lot size issue. (Smaller footprint buildings will grow on larger lot sizes, so a 5x5 lot wouldn't prevent a 4x4 skyscraper from spawning on it).
There were no industrial skyscrapers. Only commercial and residential.
For enhanced visuals, you might want to look at modded assets at Simtropolis.com, people have created some fantastic stuff. (I also seem to recall that some mods have been created there which allow skyscrapers to grow more easily, as well)