Different people have different ideas of retrogaming, I guess you can say. Some will see it purely as playing those old games from the past exclusively, others will see things like this - rom hacks - as being part of that, some others may consider games that have a retro style as being part of it as well. When it comes to what I post here, I stick to things that I think people that come here might be interested in and just let the upvotes/downvotes decide.

Valid question, but to my mind it counts because it's retro style.

Just like you can have contemporary classical music.

Delayed answer, but if anything, new releases on old consoles are actual retrograming, while just playing old games is not. "Retro" originally meant something new that was made to look old.