You could also use 'opinion' or 'viewpoint' instead of 'input'.

It's very common. I hate it. It's fully accepted. I hate it. Hate, hate, hate. It's almost certainly in the dictionary--yes, ahdictionary.org says "3. Contribution of information or a comment or viewpoint: a discussion with input from all members of the group." I hate it. I would never use it myself, because I hate it. It's a misappropriation of a technical term. Did I mention that I hate it? Because I do. And I don't like "feedback," either.

"Input" is usually used either in a professional setting, or in a group of people where there is more than one opinion. A more informal and personal way of saying it would be "viewpoint" or "opinion."

"Input" is used in that way often... usually not in a personal way. Maybe in the context of work or a non-personal activity.

I actually do. In a professional context, we even have people called Market Advisors who collects Market Inputs !