Responsive page using Flutter

I decided to try out Flutter for this challenge since it lets me create cross-platform applications. I definitely learned a lot about Flutter because of this challenge. However, I still have a ton of questions about how to optimally use Flutter. Some questions are:

1. What's an organized way of implementing a responsive UI using Flutter? I kind of took a page from what I did with my CSS by having a global root size and applying it to all my widget styles, but I'm not sure if this is an optimal way of doing so.

2. How to design a UI that also responds to a screen's orientation (landscape or portrait)? I haven't been able to implement it on this challenge since I didn't want to overload myself with too much to learn.

3. What's a good way to manage states across Flutter widgets? When I use React, I'd use Redux so that all the info I need are in one place accessible to all my components. Is there something similar in Flutter? My current solution is using providers but I'm not sure if that's the best way to go about it.

Any and all feedback is more than welcome! Cheers🎉