Thanks for all the suggestions and advice, Charlie. I appreciate your detailed and thoughtful response. I've taken all of your points into consideration, although even so I'm still planning on adding a new camera within the next few months to a year.
Your suggestions are all great, however, and I definitely agree that continuing to hone and refine my skills as a videographer is by far more important than simply what camera(s), lenses, or other gear I'm using.
I do try and practice my focus racking skills on a regular basis by having my six year old run around in our yard (he never holds still for two seconds) and seeing how long and how well I can keep him in focus manually as he runs all over the place. Your suggestions about a light cart are well-taken, although certain rooms I'm not allowed to walk into at all (I have to shoot through the very small doorways) since it's large magnet medical equipment. I do use an assistant for some shoots, but only on higher-budget ones. A lot of these shoots don't have enough budget to cover me as well as another person, but I don't mind doing them solo since I get to do more shooting which results in having more work samples (which has so far lead to more video work), and still make some decent money. And, I had a second camera (a GH3) but I just recently sold it (in part to help fund this next planned camera purchase).
Concerning the audio unit - I've never missed any audio yet (although there was one time I *thought* I had forgot to switch it on before recording and feared the worst). It's primarily a matter of convenience and concern that I could *potentially* miss audio if the battery goes out in the unit while I'm in the middle of recording (the XLR adapter unit I have uses regular 9V batteries and the low battery light on it is hard to see on it when I'm actively shooting vs. being able to monitor a single battery level in a camera's EVF/flip-out screen). Additionally, I come from using non-DSLR form-factor cameras (various Sony, Canon and JVC at past employers) where the XLR ports and audio controls were typically built in so I'm used to having most everything built into the camera vs. frankensteining stuff together the way I've done since first getting a GH3.
Having said that, I love the GH4. I like the ability to determine my own lens choices for specific shots, have the camera be inconspicuous and ultra-portable when necessary, have 4K built-in to the camera, the flexibility of looks that can be achieved in post, the ability to also take decent stills, etc., although I sometimes miss having a servo zoom.
However, I guess I just also really like the idea of having the XLR/audio features built-in to a camera similar to how many people feel about having ND filters and 4K built-in - it's simply far more convenient with less batteries and gear to carry around, and fewer switches/indicators to be concerned about in the heat of the moment, although I've been getting by just fine without some of these things since starting to shoot with the GH3 and GH4.
I do roll in the cost of my gear, time, insurance, etc., to my clients, which is why I have the funds to purchase new gear. My little GH4 has paid for itself many, many times over, and over time I've been able to build up a fairly versatile set of gear to better support the type of video work I currently do including lights, microphones, backdrops, tripods, teleprompter, etc.
I used to use a Canon HV30 back a number of years ago when I first started to shoot any video for clients on my own (mostly as a hobby, vs. for my employer at the time who had much nicer and more expensive video cameras in-house), and that is how I funded my first serious tripod and microphones, and eventually, a GH3 (which is when I started offering video as a service "officially"), which I was then able to earn enough with to fund some decent lighting gear, some additional lenses, and eventually the purchase of my GH4. At this point, I'm looking to repeat history and use what I earn from my GH4 to fund a move to a more all-in-one type of camera, but keep my GH4 to use as my second cam (or first cam, depending on the shot/s required).
That's why I've become more and more interested in (and seriously considering) the AG-DVX200 since my original posting here (especially now that there are some footage samples around), since I would imagine it might be fairly easy to match it to the GH4 in post. That way, I'd have the best of both worlds - an all-in-one unit perfect for 4K run n' gun (with a servo zoom) and quick setup shoots, but with the ability to yield a nicer image than the typical fixed lens unit in that price range, and my GH4, which would give me the ability to use variety of lenses for specific looks and that could act as either the "A" or "B" cam dependent on the shoot, and to which I could also eventually add a Speedbooster (+ lenses) to in order to emulate the Super 35 look. Plus, the DVX200 has the 120FPS capability, which is a nice bonus (although as you mentioned the GH4 does 96fps, which I've used on occasion).
Of course, the main issue would be still be low light performance in certain instances (even taking all of your suggestions into account), hence my consideration of the Canon C100 Mark II (which also has the dual-pixel autofocus). And for the green screen stuff and color grading, I'm sure the Ursa Mini 4.6K or FS7 would be superior in these areas, but as you commented, "use the cheapest gear that will get the job done."
Right now, for a more all-in-one camera solution that seems to suit the majority of the work I'm currently doing, that's starting to look more like the DVX-200 at roughly $4200 vs. the others on my list. I know someone also suggested the JVC-LS300, which I looked into a bit, but having used some JVC video cameras in that price range before, I've never been impressed with their image or build quality vs. the Canons, Sonys, or Panasonics I've had the opportunity to use. So, while it may also tick a lot of boxes, for me I think it's more of a personal preference issue with that particular brand based on past experiences.
Anyhow, while I'm still not 100% decided yet, I've become far more interested in the DVX200 at this point in time (although I am very interested yet in seeing Ursa Mini footage samples when it finally comes out and more from the DVX200, too). I appreciate all the responses so far, and per Charlie's comments, will continue to improve my skills using my current setup along the way.
Thanks for the link, Guy! Looking at the full list of specs for this video camera it seems to deliver (at least on paper) a LOT of what I'm looking for: built-in XLR, ND filters, shallow focus/nice bokeh, nice form factor, intelligent autofocus, 12 stops DR, V-Log, 4K and even 120FPS in FHD (not as sweet as FS7's 180FPS, but as good as the URSA mini), which I was not aware of–very nice!
I may have to wait this one out! Can't wait to see some footage and a few reviews of this cam-particularly low light performance. While it doesn't offer interchangeable lenses, since I plan to keep my GH4 (another Panasonic) they *might* make a great pairing, and I could use each for the stuff they're best at (DVX200 for events/run-n-gun, GH4 for more controlled shoots/green screen).