How to make Match 3 versus game AI C#?

Hello. I'm currently learning about how to make Match 3 game. I've searched in Google and found many of them, so I can easily learn the basic of making them. However, I don't have any answer to this unique one. Please take a look into this video (you can skip it into part 5:11)

https://www.youtube.com/watch?v=vJXpfik3EEI

I have a couple of question here. 1. Most of tutorials are using mouse drag system, but this one is using something like crosshair. How to perform swap with this one? 2. The opponent AI is very smart. How to make that logic? 3. How to make the board could have an empty tile and the new tiles are come slowly from the bottom? 4. You can perform several matches and combos at the same time without disrupting the others. How to script it?

I can't really get these logics. Hope you are able to answer. Thank you very much! :)