How to get chocolate flavor into my stout?

I'm currently brewing a cherry chocolate milk stout. I plan to add some cherry flavoring prior to bottling and put the lactose in while boiling the wort. My questions are: 1) when should the chocolate go in, 2) what kind to use, & 3) how much to put in?

I was under the impression that I should use chocolate nibs in the secondary about a week before bottling, but some threads state it should have been done during the boil.

Can I use cocoa powder in the secondary?

Hope I didn't mess it up, but maybe I'll experiment and put cocoa powder into the secondary anyway and see what I get.

Thanks all in advance for your help!
K.M.

I have been researching the same issue. Much like a lot of things homebrew one person will swear that the only way is to use chocolate nibs in the secondary, then the next one swears its gotta be bakers chocolate in the last 5 minutes of the boil. I am gonna go for cocoa powder at burnout. As best I could tell all of the above said they had good results. I suppose that's why it's so fun, there are only a few things in this hobby that are absolutes. Good luck.