I faced the same decision about 5 years ago. At that time, I went with an ARRI kit (slightly bigger--750W flood, 650 fresnel, 2x 300W fresnel, plus a Chimera soft box and ARRI-branded leather gloves). To this day, I feel like I should have a Kino in my bag of tricks, but I don't. And to this day, I wonder: what if I'd gone with the Kino first?
The ARRI kit makes 3-point lighting a dream, especially with the soft box. But my cameras really prefer daylight balanced light, and Kinos make that very easy. You can also get egg crate light modifiers to Kinos, which creates really great light. Finally, there are now high CRI LED fresnel lamps. Yes, they are much more expensive than halogen, but they provide daylight balance and much cooler operating temperatures.
So all in all, I would say that the Kinos are still state-of-the-art for what they do. The ARRI tungsten lamps remain a good low-end solution, but if your corporate gigs do start working out, you might be able to skip halogen and go straight to LED fresnel. BTW, I do have a pair of ARRI L7-C lamps, and they are a big reason that I hardly ever pull out the tungsten kit. And I still wish I had a large shaped source like the Kino...
Nine months ago you started a thread that generated lots of good answers: http://nofilmschool.com/boards/questions/whats-best-4k-movie-camera-unde...
Almost all that advice remains valid and on-point. Yes, there have been a few new announcements (such as the GH5) since then. But the GH5 is not shipping yet, and the GH4 remains a strong product for what it is: a low-cost, high-quality 4K camera.
The SONY A7SII remains the low-light king.
The Canon 5D4 does shoot 4K, but with all the limitations that Canon maintains to keep their DSLR line less functional than their Cx00 cinema cameras. And the 5D4 is not inexpensive. And it's not mirrorless, which means a literally large part of the camera (the SLR mechanism) is using up space that is irrelevant to your pursuits.
I have a GH4 and love it. You can make a 4K movie today with a GH4. Or you can wait for the next best thing, which is pretty might always right around the corner, but never without another options coming a little farther into the future.
Also non-sensical is that my up-votes to the above show Michael's post with a stll-zero score. Who are the trolls that doen-vote so much content each and every day? Mods should be on that, too.
I strongly recommend you read the questions and answers in this recent thread: http://nofilmschool.com/boards/questions/getting-right-exposure-post-pro...
Those answers, as well as the one above (which I upvoted to indicate its correctness), all point to the same fact: if you want a good image, you have to light and expose properly. If you don't (because you don't have the right equipment or you won't rent the right equipment), you are making a compromise that will result in reduced image quality. When you over-expose, you cheat yourself out of good color as highlights burn out. When you under-expose, you bring noise into the shadows, which can become devastating in a low-key shot. When you light and expose correctly, you can get a good image, which then gives you something to work with in post.
Cameras with high-sensitivity sensors (like the SONY A7 and the EPIC-W) allow one to shoot with less overall light, but if you use those cameras and look at proper exposure meters, the reason they produce a better image with less light is because they are calibrated to deliver middle-tone gray with less total light. In other words, if you use such cameras, and proper metering, you will see that it's not about over-exposing highlights or under-exposing shadows. It's about proper lighting and exposure from the start.
A recent phrase I heard is "light your subject, not the set". Translated, what this means is that when you are building a low-key scene, you must make sure that your subject has all the light it needs, preferably at an ISO you can live with. If it's two people talking at a dark and smokey bar, then step one is meter their faces at the table and make sure you have all the light you need to have proper highlights and midtones on the faces. Once you have that, then you can meter the set, and if it's generally more than 3-4 stops darker than your mid-tone gray, then you might also want to add some lights. Or if it's generally less than 2-3 stops below, you might want to take some lights away and/or darken up the objects in the scene (with black tablecloths instead of white, etc).
Metering the shadows of a low-key scene and then trying to recover highlights from your subject is not a good approach, as you have discovered.
You should make your short film first, then study closely whether your lens is your limiting factor, or whether your camera, lighting, sound, editing, grading, script, acting, wardrobe, etc. is most in need of an upgrade. If lens quality really is your weak link, then by all means make the investment. By you cannot really make the decision by just thinking about it. You have to produce work, critically evaluate it, and then make decisions based on actual experience.