At the point where you have a large distribution channel,there is a camera budget and your personal gear is no longer a liability.

" I could invest in gear that will be more long term and learn how to create compelling footage with what I have that pleases clients, then upgrade my camera body in the future "

This. Even if your marketability is temporarily hurt because you don't have the latest buzzword it's all about compelling images. Even lots of big budget work is still in 2k. 4k footage is still a nice to have, not a must for most work.

If you really need 4k for a job, rent a camera body that works with your existing gear. Have a rental place in mind, with a specific package that you know the cost of. That way you can run all of the numbers and see if you can charge enough extra to make the cost of renting a body for the project work out.

In a broader sense, it was the exception that set the rule. Cinematography has an ebb and flow in styles.

Before Toland made lens coating for 'Citizen Kane' everything has flare. After that it was pretty accepted to shoot sharp and flare free as possible. "Easy Rider" made it acceptable and popular to have in camera flare again. It will eventually swing back towards sharp and high contrast . Experimentation helps breed creativity.

Analog flares can be quite hard to reproduce digitally and if that is part of the intended look then that is great. I can't imagine trying to add the lens flares back in "Hateful Eight" in a digital fashion.

Your advice seemed quite aggressive for such a normal question. It doesn't seem like poor choices are being made on the lens front.There is quite a difference between a DP asking for some assistance in making lenses less sharp, and needing a piece of 60's glass. The lenses mentioned in the post are pretty sharp on their own and good quality. A little bit of diffusion goes a long way from making something look clinical to natural.

This is a great video to show the practical needs for all of the special qualities of a cinema zoom vs a still zoom. Kudos!

It also accidentally shows the need for monitoring audio during the shoot and high quality scratch audio. A good on camera shotgun would have saved the interview.

It sounds like you are shooting a piece that is going to have normal time as well as slow motion time. You have 2 decisions to make,the second is based on the first.

What frame rate should you shoot at?
This can depend on equipment. Typically the film 'look' is shooting 24FPS at a 180 degree shutter. That results in a 1/48th of a second exposure time per-frame.
You can shoot at true 24fps with a 180 degree shutter and have youtube deal with it.If your camera rates shutter in terms of speed 1/48th.

You can get a similar feel by shooting at 30fps and having an exposure per fame of 1/48th, or if your camera goes by shutter angle about 225.

For YouTube I am not sure how much difference it makes. It may be simpler to shoot 30fps if your camera can support it. If it can't, shoot 24fps and let youtube convert the frame rate for you.

Next determine what your time dilation is? I.e. how much screen time will real time take? So should 1 real second take 1.5 seconds, 2 second, 3 seconds etc?

If 1 second of real time should take 2 second you need to double your record rate, so record 48fps for 24 and 60fps for 30. Likewise 72 fps for 3 seconds at 24 and 90 for 3 seconds at 30.

Does this make any kind of sense?

Didn't the flare fad start with Laszlo Kovacs in "Easy Rider?"