Choose a format by what your idea needs, not by what looks impressive. Interviews suit one person with direct knowledge. Documentaries suit stories rooted in a place. Panels suit genuinely contested questions. Explainers suit things people misunderstand. Personal stories suit experience nobody else can report. Cost and difficulty vary enormously between them.
A recorded interview, or an explainer you present yourself. Both need one room and no access negotiations, and the quality depends mostly on preparation rather than equipment. Documentaries are the most budget-sensitive because access and travel dominate.
Interviews commonly run twenty to forty minutes, explainers five to fifteen, documentary segments ten to thirty, panels thirty to sixty. These are conventions rather than rules, and a shorter piece that holds attention beats a longer one that does not.
Often yes, and it becomes a different piece in each. The same subject as an interview centres one person judgement; as a documentary it centres a place; as a panel it centres a disagreement. Choosing between them is an editorial decision, not an administrative one.
Indirectly. A format that clearly suits the idea makes the proposal easier to imagine as a finished programme, and proposals people can picture tend to attract more support than ones that require the reader to do that work.