Today, you can get very powerful overheads from Blackmagic Design, Datavideo, Livestream, Panasonic and others at minimal cost. For larger projects you will also need an intercom, a multiviewer (some of \the overheads of course offer sufficient multiview outputs), a keying background, or a control panel.
A video standards converter or splitter is an absolute must, whether you're working with consumer HDMI or professional 3G/6G/12G-SDI gear. Modern wireless video transmission systems are a special chapter, which will be appreciated by filmmakers (focus, overhead, etc.), drone operators or news teams.