What style, scenes, distances between the shooting position and the subjects? I would recommend a Z mount S lens. If you are doing grand vistas or more than one person at fairly close quarters the 24mm 1.8 or if decent light, the 24-70 f/4 is not only a bargain, quiet and very good corner to corner sharpness. IF you have that zoom, you have all you need to start..
So much depends on your topics. The zoom allows very close working distance if B roll is needed for detail close ups. By switching to Dx mode, effective field of view of a 105mm telephoto for details of more distant subjects.
The most expensive added piece of gear will be a stabilization system. There are weight passive stabilizers that are very effective for those shots that stay on the same plane. If dynamic movement of orientation, rotating on a axis perpendicular to horizon or rolling than a much more expensive motorized 3 axis gimbal is needed. A lot can be done with just a tripod for smooth pans. You might save lot of money by not getting a 3 axis motorized gimbal at the beginning until getting enough experience to figure out your style. If you are following skate boarders on a skate board. yeah, you need a quality high torque gimbal. If you are just walking to track someone walking a weight passive cheap stabilizer is plenty good enough.
If there is live sound to be recorded, a low cost multichannel digital recorder can be very useful and not depending on the sound from the camera recorder because sound recorded close to the source should be #1 rule to make sure sound does not ruin a production. Even with a $5000 mic, recording from 15 feet away will be usually hardly usable while a $2 mic close, within 18 inches of the source will be perfectly competent. That will require wireless mics on the talent, and receivers, or a boom operator with a overhead out of frame mic. Few beginning video production efforts consider the importance of audio quality(meaning diminished levels of ambient sound, reflected sound and reverberant fields that destroys intelligibility.
The best editing suite for free is DaVinci Resolve 16. But any editing suite is a processor workload that calls for a pretty powerful video processor and main processor.
If you are doing anything in dim light the Z6 is pretty darn good at high ISO but consider some continuous lighting. You can make LED panels that can be made of strips of equalized LED of a wide variety of color temperatures.