Who should I get letters of recommendation from?

I'm already looking into my second year internship placement options, and will begin applying in Jan/Feb. Some of the options I'm most interested in ask for 3-4 letters of recommendation, though most ask for 1-2.

I do have options, but I'm (overthinking) who to ask. I work in my school's online office, so I have contact with the Dean of the online program, the Director for the social work program, and the director of enrollment is my direct supervisor. I also have a great relationship with two assistant deans.

At my current placement, I have my supervisor who I plan to get a letter from, but I don't really have much contact with other staff because everyone is mostly virtual still. I have met the owner of the practice, and while I'm sure he'd write a letter, it might be pretty generic (he joked about how he's too old to get to know each class of interns every year).

Would any of these be better than the rest? Like, will it be more important to have letters from staff therapists? Or would it be impressive to have Dean letters?

And, finally, is it kosher to ask for an unaddressed copy so I can just send it out with each file? Or would I want to narrow things down and ask the person to send it to each org?

I know this is dumb, so thanks for the advise! Haha