Six things to consider:
1) Camera settings. When shooting video, the camera encodes and compresses it as you record. This is like shooting jpeg instead of raw - meaning, it's important to get the exposure and white-balance right in camera. Use a picture style that suits the look that you want. Use an appropriate shutter speed - even though the shutter isn't actually opening and closing like it does with still images, your shutter speed WILL affect the way the video looks - if the shutter speed is very fast, the video will have a certain "look" that's hard to describe, almost like a stop-motion video. Good for gritty action sequences, bad for just about anything else.
1a) If in doubt, use 1/50 if you're using 24fps video encoding, and 1/60 if you're using 30fps video encoding. Set it and forget it. Adjust your exposure with aperture, ISO, and neutral-density filters - NOT by shutter speed.
1b) If you use the Magic Lantern firmware, you can shoot raw video. However, if your video editing person isn't expecting this, don't do it.
1c) A workable approximation to shooting raw, is to use certain picture styles (e.g. Kodak Cinestyle) that will capture more dynamic range. However, these will make video that looks flat and boring without proper editing.
2) Focusing. I don't know if the 5D4 has improved over previous Canons, but video focusing is one area where DSLRs fail miserably. No good advice here. Autofocus for still images simply doesn't apply for video - while the mirror is up, the usual autofocus system is unavailable,. You can try the live-view autofocus but don't get your hopes up.
An external focusing screen kinda helps. Focus Peaking in the Magic Lantern firmware helps. Having subject matter that doesn't move .. yeah, that's actually the best solution, just don't shoot video of moving subjects
3) Audio. Your audio gear depends on your budget and your style of shooting. The on-camera mic is practically unusable - however, you don't always need to record audio, just put a music track or a voiceover on it later. If you DO want to record audio, at a minimum you'll put a little battery-powered shotgun mic on the camera's hotshoe - I think we have an entry-level Rode shotgun mic for this. If you're going interview-style videos and want to cleanly record voices, a "lavalier" lapel mic is an easy and reliable solution. For wireless lavaliers, we use Sony UTX but these may be overkill for someone just starting out. We used to have some cheap lavaliers but they were terrible and unreliable, I can't really recommend any cheap ones - I'm sure they're out there, but I don't know them.
4) Lighting. When you're just starting out, the concept is not too different from photographic lighting. Look for good light, or make your own. Direct sun is usually bad. We use a cheap-and-flimsy DayFlo fluorescent lighting kit, and/or the Digital Juice MiniBurst LED lights.
5) Camera Support. A DSLR is absurdly UN-ergonomic for shooting video. For fixed video (interviews, fixed non-panning camera to record a wedding ceremony, etc), your photo tripod is plenty. If you want to pan around, a fluid-head video tripod is necessary. If you want to carry the camera around, there are a bunch of different solutions: From a shoulder mount, to a simple weighted stabilizer, to a full body-harness Steadicam system. We had a harness-based Steadicam but rarely used it, it was just overkill for the style of video we do. Now we use a Benro fluid-head tripod (can't remember the model number), or a relatively inexpensive Digital Juice brand weighted stabilizer. Also have a shoulder mount that's rarely used.
I think this is our stabilizer, I don't see it in their store any more, but there are a bunch of similar offerings from competitors:
6) Editing. As a general rule, shoot three to ten times as much as you think you'll need, then edit it down. Just like nobody wants to see your blurry out-of-focus still photos, nobody wants to watch minutes and minutes of boring video footage. Editing software varies by operating system, budget, and skill level. I just hand all this off to my wife, she's been doing this for [redacted number] years.