How to add the custom features to orders list page in Admin

Hello world, since I am really new to Shopify I might be asking something really stupid or impossible or both, but this time I need to figure out some technical possibilities for my client.

This time, my client asked me to implement the new features to their own site, which is adding comments on the orders list page and add the features to the “more action” button and opens it with two new function “add comments” and “remove comments”.

(I have attached images I created)

My focus is

1, whether this adding new features to “more actions” button is feasible or not.

2, if possible where should I start with ?( e.g. editing theme or API (probably not), when it’s about theme, which file should I try to edit on?)

3, Basically, what they want to do is to add comments to each order so that the customer can see the comments from the shop. and the shop can add the comments to multiple comments at the same time, because they think comments from shop doesn’t need to have several variations but just two or three. So if there is any feasible solution, please also tell me about it.

Since it seems there are not anyone trying to do something like this, I might be asking silly question, but any comments are welcome. Please give me your knowledge. Thank you.

Best regards,

Kofsaku