Mostly agree with the others. dp to HDMI 2.0 "Active" adaptor is required to get you 4K 60Hz. I use my 84" 4K TV as monitor as well. But not for the main OSX operation, I do the "usual stuff' on my 27" ACD. but only use that TV for pictures / 4K video editing preview, etc (something work better on large screen, but not require multiple quick precise mouse pointer action). I am totally OK with on 30Hz on that screen. But in general, 60Hz is much much better for monitor.
For distance, it depends on what you want. Since I want to use my TV to check the details, therefore I use it only 2' away from me. TBH, there is no way that I can see the whole screen at once. It's just far too big, but that's how I use it. I can only clearly see all the small details when I am very close to the TV. When gaming, I will seat 10-15' away from it.
Few more points why TV is generally not good for monitor.
1) Unless the TV provide accurate colour calibrating function. The colour may be very wrong. They usually much more rich then what it should be. That's how the manufacture make the public feel their TV is good (rich colour usually looks nicer). But usually only the top of the line TV have these kind of function. Normal TV only has simple colour tuning ability, hard to perform as good as monitor on accurately display the original colour.
2) Input lag is high. Most flat TV offer computer / game mode to reduce input lag (which may further reduce the colour correcting ability). However, the input lag may still 3x or even 10x of a monitor can do. Which will may you extremely hard to have accurate mouse movement.
3) TV usually has lots of post processing, some functions may able to turn off directly, some others may able to turn off by using game / computer mode. However, some functions may not able to turn off. Which may cause the TV unable to accurate display the image. e.g. May be the icon looks a little bit different on the TV then your screen, because the TV add some artificial sharpness / noise canceling on the icon.
Since you said that you use it for photoshop. I can tell you that's a good way to get a big 4K screen that allow you to see the details. However, a very bad way to accurately display the picture. Unless you know that TV model can turn off all the post processing function AND the colour correcting function can work in computer / game mode.
In general, colour may not be a big problem, because you can still use something like spider to calibrate the colour from the computer side. However, post processing may kill you. You want the TV allow you to see the details, but it only display the "processed detail", which most likely not your original intention. And TBH, this may make your "able to see the details" become meaningless, because you still can't see the original details.
