English opening

Yes

yes. it was a favorite of Victor Krochnoi.

Depends, there are a lot of transpositions and may be hard to decide when to break away from English territory.

As an example, an immediate d4 can transpose to a Catalan but d3 keeps things in Reversed Dragon territory.

Then there’s the Botvinnik System you should learn since it has it place but it’s truly not a one size fits all opening system.

I would recommend you play the Sicilian to double your practice if you do go the English route.

Due to the transpositional nature I feel like the English will be more suited to someone who knows many other openings and plays at a high level. That way they can know what they're transposing into and won't get caught out, may even benefit by having a move in hand or playing black a move up as can happen sometimes.

The English is also a complex opening and can be hard to push for an advantage. You can't just go into it and expect to end up with the computer saying white has an advantage. There's a reason why it was ignored for centuries by the best chess players in the world until Staunton came along and revived it. So I would prefer someone be knowledgeable at d4 first.

Uh oh spaghettio 1, has a point. to play the English you do need to have a basic understanding of d4 style games. some times switching to d4 is better. like against the KID. Or changing to the Catalan. or simply to avoid the Nimzo and going back to a d4 game.

I prefer 1. Nf3