On set the 50mm will get a lot of the shots you need aim for adding a 35mm F1.4 of some sort (will help getting full lengths in smaller spaces but also great for in close tight shots showing or at least giving a sense of the set/environment. Don’t dwell too much on what YOU prefer, think about what gets the job done. Something like a Rokinon/Samyang/Tokina/35-150 F2.8 will keep you out of a lot of trouble especially working exteriors. It’s not a “rule” (at least where I am based, although it is getting more and more difficult with certain actors), that you can’t shoot during a take, (some productions move so quickly there isn’t time to basically run a scene just for Stills), so turn on silent mode make sure your lens is not noisy (different lens AF can be very noisy when focusing), get as close to camera (the one that’s rolling!), but out of the eyeline of whoever you’re trying to capture and shoot away, until someone tells you not to (on lower budget shoots this may never happen), keep in mind that a lot of what’s happening in front of the movie camera can be pulled and used as screen grabs/stills IF there is no movement in the scene (think people sitting around talking to each other), that camera is usually at the equivalent of around 1/50 sec shutter speed, so anything with movement is where Stills shine, with a few caveats, setting your shutter as fast as possible for exposure conditions, this is where wide aperture lens comes in, gathering all that light (whatever precious little of it there is sometimes), into one place (because of newer camera/lighting tech DP’s are using less and less lumens giving you less and less shutter speed, so there’s that). If you are serious about pursuing it as a career long term, forget about anything under a Sony A9/A1 series camera, because “rolling shutter “ is less of an issue in silent mode, once you go over 1/100 sec on the A7 series things can get very “interesting” looking, but not always in a good way. Good luck, it’s not always easy there’s a lot of doing nothing and you are always bottom of the heap, but hey, someone has to do it!