> The possibility that you might ask to call has no bearing on whether or not you should start with "Hello," because if you are going to ask to call, you would be better served by just asking to call

If they respond (within a minute, say), you might ask for a call. If they don't, you instead type out the question, and check back later. Hence the response (asking for call, vs question) depends on the answer to "Hi".

> if you are going to send the message to multiple people, you would be better served by sending your actual question

Why? If someone else is answering, I explicitly don't want another person to start working on the question. If anyone one responds while I've already asked the question, I can just tell them I no longer need help - they waste little to no time or focus working on finding an answer.

> Even if you get more than one answer, you can just thank the people for their responses

This seems like a much bigger waste of other peoples time.

> you are still better served by having them know why you wanted to talk, since they can better appreciate why you would have sent multiple messages

why am I "better served" by this? They don't need to know what I might have asked, it's a distraction for them.

> if you do need someone to be present, you would be better served by having them already know what you might need them to be present to discuss

If they aren't present, the discussion may not happen.