Bimlendu K.

For optimizing performance there are certain things that we should consider:
1. adding caching

2. Adding lazy loaded modules

3. compressing images on server as well as frontend using third party libraries, also lazyload images

4. css file optimization during build

5. less touching DOMs directly use SPAs concepts made for that

6. using websockets

These are most common ways to optimise applications now a days

4. using paginations - if requirement is there

5. 

ReactJS does not much depend on editor. But still visual studio is the best choice.

But you should more focus on is React extenstions in browser.
It helps you to understand and visualize the Tree structure of component.

It also helps you to see the list of props and states added to the component and with the values against each of them.
So as developer we should combine visual studio code as well as browser extensions to be more expert in React.

State is used to control the lifecycle in React.
When state changes then based on provided inputs render of component happens.

In simple ways State represents the identity of component that how component will render. We can control it also using useEffect() hook.
Whereas props are properties that we pass from parent to child.
On props change, whole tree below it will rerender and we can control it only till a certain level.
State also represents lifecyle including mount, render and destroy and we can control it. But props re-renders everything as soon as it changes.

No. And I shall tell you the reason.
React is open library whereas Angular is framework.
Because of being library, it integrate important other libraries so it makes application more accurate, more testable.
Also React works on Virtual DOM concept whereas Angular works on Shadow DOM so again performance wise React will always be better than Angular.

Lifecycle: React follows only mounting, rendering and destroy lifecycle whereas Angular uses changeDetection() lifecycle and weight wise React's lifecycle is really lightweight than angular.
So React can not be replaced by angular anyway. :) 
Hope this gives a good answer for your query.